Waveguide device, slot array antenna, and radar, radar system, and wireless communication system including the slot array antenna

ABSTRACT

A waveguide device includes: an electrically conductive member having an electrically conductive surface; a waveguide member having an electrically-conductive waveguide face of a stripe shape opposing the electrically conductive surface, the waveguide member extending along the electrically conductive surface; and an artificial magnetic conductor extending on both sides of the waveguide member. The waveguide member has a bend at which the direction that the waveguide member extends changes. A waveguide which is defined by the electrically conductive surface, the waveguide face, and the artificial magnetic conductor includes a gap enlargement where a gap between the electrically conductive surface and the waveguide face is locally increased. In a perspective view along a direction perpendicular to the electrically conductive surface, at least a portion of the bend has an overlap with the gap enlargement.

BACKGROUND

1. Technical Field

The present disclosure relates to a waveguide device, and an antennadevice including the waveguide device.

2. Description of the Related Art

Examples of waveguiding structures including an artificial magneticconductor are disclosed in Patent Documents 1 to 3 and Non-PatentDocuments 1 and 2 as follows.

-   Patent Document 1: International Publication No. 2010/050122-   Patent Document 2: the specification of U.S. Pat. No. 8,803,638-   Patent Document 3: the specification of European Patent Application    Publication No. 1331688-   Non-Patent Document 1: H. Kirino and K. Ogawa, “A 76 GHz    Multi-Layered Phased Array Antenna using a Non-Metal Contact    Metamaterial Waveguide”, IEEE Transaction on Antenna and    Propagation, Vol. 60, No. 2, pp. 840-853, February, 2012-   Non-Patent Document 2: A. Uz. Zaman and P.-S. Kildal, “Ku Band    Linear Slot-Array in Ridge Gapwaveguide Technology, EUCAP 2013, 7th    European Conference on Antenna and Propagation

An artificial magnetic conductor is a structure which artificiallyrealizes the properties of a perfect magnetic conductor (PMC), whichdoes not exist in nature. One property of a perfect magnetic conductoris that “a magnetic field on its surface has zero tangential component”.This property is the opposite of the property of a perfect electricconductor (PEC), i.e., “an electric field on its surface has zerotangential component”. Although no perfect magnetic conductor exists innature, it can be embodied by an artificial structure, e.g., an array ofa plurality of electrically conductive rods. An artificial magneticconductor functions as a perfect magnetic conductor in a specificfrequency band which is defined by its structure. An artificial magneticconductor restrains or prevents an electromagnetic wave of any frequencythat is contained in the specific frequency band (propagation-restrictedband) from propagating along the surface of the artificial magneticconductor. For this reason, the surface of an artificial magneticconductor may be referred to as a high impedance surface.

In the waveguide devices disclosed in Patent Documents 1 to 3 andNon-Patent Documents 1 and 2, an artificial magnetic conductor isrealized by a plurality of electrically conductive rods which arearrayed along row and column directions. Such rods are projections whichmay also be referred to as posts or pins. Each of these waveguidedevices includes, as a whole, a pair of opposing electrically conductiveplates. One conductive plate has a ridge protruding toward the otherconductive plate, and stretches of an artificial magnetic conductorextending on both sides of the ridge. An upper face (i.e., itselectrically conductive face) of the ridge opposes, via a gap, aconductive surface of the other conductive plate. An electromagneticwave of a wavelength which is contained in the propagation-restrictedband of the artificial magnetic conductor propagates along the ridge, inthe space (gap) between this conductive surface and the upper face ofthe ridge.

SUMMARY

In a waveguide such as an antenna feeding network, a waveguide membermay have a bend(s). At a bend, a change occurs in the direction that thewaveguide member extends. At such a bend, unless remedied, an impedancemismatching would occur, thus causing unwanted reflection of apropagating electromagnetic wave. Such reflection would not only cause apropagation loss in the signal, but also induce unwanted noises.

An embodiment of the present disclosure provides a waveguide device withan enhanced degree of impedance matching at a bend of a waveguidemember.

A waveguide device according to an implementation of the presentdisclosure includes: an electrically conductive member having anelectrically conductive surface; a waveguide member having anelectrically-conductive waveguide face of a stripe shape opposing theelectrically conductive surface, the waveguide member extending alongthe electrically conductive surface; and an artificial magneticconductor extending on both sides of the waveguide member, wherein, thewaveguide member has a bend at which the direction that the waveguidemember extends changes; a waveguide which is defined by the electricallyconductive surface, the waveguide face, and the artificial magneticconductor includes a gap enlargement where a gap between theelectrically conductive surface and the waveguide face is locallyincreased; and, in a perspective view along a direction perpendicular tothe electrically conductive surface, at least a portion of the bend hasan overlap with the gap enlargement.

According to an embodiment of the present disclosure, in at least aportion of a bend of a waveguide member, the gap between the conductivesurface and the waveguide face is enlarged. As a result, the degree ofimpedance matching at the bend of the waveguide member can be enhanced.

These general and specific aspects may be implemented using a system, amethod, and a computer program, and any combination of systems, methods,and computer programs.

Additional benefits and advantages of the disclosed embodiments will beapparent from the specification and Figures. The benefits and/oradvantages may be individually provided by the various embodiments andfeatures of the specification and drawings disclosure, and need not allbe provided in order to obtain one or more of the same.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a perspective view schematically showing a non-limitingexample of the fundamental construction of a waveguide device.

FIG. 2A is a diagram schematically showing a construction for awaveguide device 100, in a cross section parallel to the XZ plane.

FIG. 2B is a diagram schematically showing another construction for thewaveguide device 100 in FIG. 1, in a cross section parallel to the XZplane.

FIG. 3 is another perspective view schematically illustrating theconstruction of the waveguide device 100, illustrated so that thespacing between a conductive member 110 and a conductive member 120 isexaggerated for ease of understanding.

FIG. 4 is a diagram showing an exemplary range of dimension of eachmember in the structure shown in FIG. 2A.

FIG. 5A schematically shows an electromagnetic wave that propagates in anarrow space, i.e., a gap between a waveguide face 122 a of a waveguidemember 122 and a conductive surface 110 a of the conductive member 110.

FIG. 5B is a diagram schematically showing a cross section of a hollowwaveguide 130.

FIG. 5C is a cross-sectional view showing an implementation in which twowaveguide members 122 are provided on the conductive member 120.

FIG. 5D is a diagram schematically showing a cross section of awaveguide device in which two hollow waveguides 130 are placedside-by-side.

FIG. 6 is a diagram showing an exemplary construction in which an outercorner of a bend of a microstrip line is cut off.

FIG. 7 is a perspective view showing the structure of a ridge waveguidewhich is disclosed in Non-Patent Document 2.

FIG. 8A is a perspective view schematically sowing a partialconstruction of a waveguide device according to Comparative Example.

FIG. 8B is a diagram showing a diagram showing the construction of FIG.8A, from which a plurality of conductive rods 124 have been removed.

FIG. 8C is a diagram showing an equivalent circuit of the waveguidestructure shown in FIG. 8A.

FIG. 9A is a perspective view schematically showing a partial structureof a waveguide device according to Embodiment 1.

FIG. 9B is an upper plan view showing the structure of FIG. 9A as viewedfrom the Z direction.

FIG. 9C is a diagram showing the structure of FIG. 9A, from which aplurality of conductive rods 124 have been removed.

FIG. 9D is a diagram showing an equivalent circuit of a ridge waveguideshown in FIG. 9A.

FIG. 10A is a perspective view showing a partial structure of thewaveguide device of Embodiment 2.

FIG. 10B is an upper plan view showing the structure of FIG. 10A asviewed from the Z direction.

FIG. 10C shows the structure of FIG. 10A, from which a plurality ofconductive rods 124 have been removed.

FIG. 10D is a diagram showing enlarged a construction near a bend 136 ofa waveguide member 122.

FIG. 10E is a diagram showing enlarged another construction near a bend136 of a waveguide member 122.

FIG. 10F is a diagram showing enlarged still another construction near abend 136 of a waveguide member 122.

FIG. 10G is a diagram showing an equivalent circuit of a ridge waveguideshown in FIG. 10A.

FIG. 11 is a graph showing results of a simulation according toEmbodiment 2.

FIG. 12A is a diagram showing a first variant of a structure near a bend136 of a waveguide member 122.

FIG. 12B is a diagram showing a second variant of a structure near abend 136 of a waveguide member 122.

FIG. 12C is a diagram showing a third variant of a structure near a bend136 of a waveguide member 122.

FIG. 12D is a diagram showing a fourth variant of a structure near abend 136 of a waveguide member 122.

FIG. 12E is a diagram showing a fifth variant of a structure near a bend136 of a waveguide member 122.

FIG. 13 is a perspective view schematically showing another variant ofthe waveguide device.

FIG. 14A is a cross-sectional view showing an exemplary structure whereonly a waveguide face 122 a, defining an upper face of the waveguidemember 122, is electrically conductive, while any portion of thewaveguide member 122 other than the waveguide face 122 a is notelectrically conductive.

FIG. 14B is a diagram showing a variant in which the waveguide member122 is not formed on the conductive member 120.

FIG. 14C is a diagram showing an exemplary structure where theconductive member 120, the waveguide member 122, and each of theplurality of conductive rods 124 are composed of a dielectric surfacethat is coated with an electrically conductive material such as a metal.

FIG. 14D is a diagram showing an exemplary structure in which dielectriclayers 110 b and 120 b are respectively provided on the outermostsurfaces of conductive members 110 and 120, a waveguide member 122, andconductive rods 124.

FIG. 14E is a diagram showing another exemplary structure in whichdielectric layers 110 b and 120 b are respectively provided on theoutermost surfaces of conductive members 110 and 120, a waveguide member122, and conductive rods 124.

FIG. 14F is a diagram showing an example where the height of thewaveguide member 122 is lower than the height of the conductive rods 124and a conductive surface 110 a of the conductive member 110 protrudestoward the waveguide member 122.

FIG. 14G is a diagram showing an example where, further in the structureof FIG. 14F, portions of the conductive surface 110 a that oppose theconductive rods 124 protrude toward the conductive rods 124.

FIG. 15A is a diagram showing an example where a conductive surface 110a of the conductive member 110 is shaped as a curved surface.

FIG. 15B is a diagram showing an example where also a conductive surface120 a of the conductive member 120 is shaped as a curved surface.

FIG. 16A is an upper plan view showing an array antenna according to anembodiment of the present disclosure as viewed from the z direction.

FIG. 16B is a cross-sectional view taken along line B-B in FIG. 16A.

FIG. 17A is a diagram showing a planar layout of waveguide members 122Uin a first waveguide device 100 a.

FIG. 17B is a diagram showing a planar layout of waveguide members 122Lin a second waveguide device 100 b.

FIG. 18 shows a driver's vehicle 500, and a preceding vehicle 502 thatis traveling in the same lane as the driver's vehicle 500.

FIG. 19 shows an onboard radar system 510 of the driver's vehicle 500.

FIG. 20A shows a relationship between an array antenna AA of the onboardradar system 510 and plural arriving waves k.

FIG. 20B shows the array antenna AA receiving the k^(th) arriving wave.

FIG. 21 is a block diagram showing an exemplary fundamental constructionof a vehicle travel controlling apparatus 600 according to the presentdisclosure.

FIG. 22 is a block diagram showing another exemplary construction forthe vehicle travel controlling apparatus 600.

FIG. 23 is a block diagram showing an example of a more specificconstruction of the vehicle travel controlling apparatus 600.

FIG. 24 is a block diagram showing a more detailed exemplaryconstruction of the radar system 510 according to this ApplicationExample.

FIG. 25 shows change in frequency of a transmission signal which ismodulated based on the signal that is generated by a triangular wavegeneration circuit 581.

FIG. 26 is a diagram showing a beat frequency fu in an “ascent” periodand a beat frequency fd in a “descent” period.

FIG. 27 is a diagram showing an exemplary implementation in which asignal processing circuit 560 is implemented in hardware including aprocessor PR and a memory device MD.

FIG. 28 is a diagram showing a relationship between three frequenciesf1, f2 and f3.

FIG. 29 is a diagram showing a relationship between synthetic spectra F1to F3 on a complex plane.

FIG. 30 is a flowchart showing the procedure of a process of determiningrelative velocity and distance.

FIG. 31 is a diagram concerning a fusion apparatus in which a radarsystem 510 having a slot array antenna and an onboard camera system 700are included.

FIG. 32 is a diagram illustrating how placing a millimeter wave radar510 and an onboard camera system 700 at substantially the same positionwithin the vehicle room may allow them to acquire an identical field ofview and line of sight, thus facilitating a matching process.

FIG. 33 is a diagram showing an exemplary construction for a monitoringsystem 1500 based on millimeter wave radar.

FIG. 34 is a block diagram showing a construction for a digitalcommunication system 800A.

FIG. 35 is a block diagram showing an exemplary communication system800B including a transmitter 810B which is capable of changing its radiowave radiation pattern.

FIG. 36 is a block diagram showing an exemplary communication system800C implementing a MIMO function.

DETAILED DESCRIPTION

Prior to describing embodiments of the present disclosure, findings thatform the basis of the present disclosure will be described.

A ridge waveguide which is disclosed in each of the aforementionedPatent Document 1, Non-Patent Document 1, etc., is provided in a waffleiron structure which functions as an artificial magnetic conductor. Aridge waveguide in which such an artificial magnetic conductor isutilized based on the present disclosure (which hereinafter may bereferred to as a WRG: Waffle-iron Ridge waveGuide) is able to realize anantenna feeding network with low losses in the microwave or themillimeter wave band.

FIG. 1 is a perspective view schematically showing a non-limitingexample of a fundamental construction of such a waveguide device. FIG. 1shows XYZ coordinates along X, Y and Z directions which are orthogonalto one another. The waveguide device 100 shown in the figure includes aplate-like first conductive member 110 and a plate-like secondconductive member 120, which are in opposing and parallel positions toeach other. A plurality of conductive rods 124 are arrayed on theconductive member 120.

Note that any structure appearing in a figure of the present applicationis shown in an orientation that is selected for ease of explanation,which in no way should limit its orientation when an embodiment of thepresent disclosure is actually practiced. Moreover, the shape and sizeof a whole or a part of any structure that is shown in a figure shouldnot limit its actual shape and size.

FIG. 2A is a diagram schematically showing the construction of a crosssection of the waveguide device 100 in FIG. 1, taken parallel to the XZplane. As shown in FIG. 2A, the conductive member 110 has a conductivesurface 110 a on the side facing the conductive member 120. Theconductive surface 110 a has a two-dimensional expanse along a planewhich is orthogonal to the axial direction (Z direction) of theconductive rods 124 (i.e., a plane which is parallel to the XY plane).Although the conductive surface 110 a is shown to be a smooth plane inthis example, the conductive surface 110 a does not need to be a plane,as will be described later.

FIG. 3 is a perspective view schematically showing the waveguide device100, illustrated so that the spacing between the conductive member 110and the conductive member 120 is exaggerated for ease of understanding.In an actual waveguide device 100, as shown in FIG. 1 and FIG. 2A, thespacing between the conductive member 110 and the conductive member 120is narrow, with the conductive member 110 covering over all of theconductive rods 124 on the conductive member 120.

See FIG. 2A again. The plurality of conductive rods 124 arrayed on theconductive member 120 each have a leading end 124 a opposing theconductive surface 110 a. In the example shown in the figure, theleading ends 124 a of the plurality of conductive rods 124 are on thesame plane. This plane defines the surface 125 of an artificial magneticconductor. Each conductive rod 124 does not need to be entirelyelectrically conductive, so long as it at least includes an electricallyconductive layer that extends along the upper face and the side face ofthe rod-like structure. Although this electrically conductive layer maybe located at the surface layer of the rod-like structure, the surfacelayer may be composed of an insulation coating or a resin layer with noelectrically conductive layer existing on the surface of the rod-likestructure. Moreover, each conductive member 120 does not need to beentirely electrically conductive, so long as it can support theplurality of conductive rods 124 to constitute an artificial magneticconductor. Of the surfaces of the conductive member 120, a face 120 acarrying the plurality of conductive rods 124 may be electricallyconductive, such that the electrical conductor electricallyinterconnects the surfaces of adjacent ones of the plurality ofconductive rods 124. Moreover, the electrically conductive layer of theconductive member 120 may be covered with an insulation coating or aresin layer. In other words, the entire combination of the conductivemember 120 and the plurality of conductive rods 124 may at least presentan electrically conductive layer with rises and falls opposing theconductive surface 110 a of the conductive member 110.

On the conductive member 120, a ridge-like waveguide member 122 isprovided among the plurality of conductive rods 124. More specifically,stretches of an artificial magnetic conductor are present on both sidesof the waveguide member 122, such that the waveguide member 122 issandwiched between the stretches of artificial magnetic conductor onboth sides. As can be seen from FIG. 3, the waveguide member 122 in thisexample is supported on the conductive member 120, and extends linearlyalong the Y direction. In the example shown in the figure, the waveguidemember 122 has the same height and width as those of the conductive rods124. As will be described later, however, the height and width of thewaveguide member 122 may have different values from those of theconductive rod 124. Unlike the conductive rods 124, the waveguide member122 extends along a direction (which in this example is the Y direction)in which to guide electromagnetic waves along the conductive surface 110a. Similarly, the waveguide member 122 does not need to be entirelyelectrically conductive, but may at least include an electricallyconductive waveguide face 122 a opposing the conductive surface 110 a ofthe conductive member 110. The conductive member 120, the plurality ofconductive rods 124, and the waveguide member 122 may be parts of acontinuous single-piece body. Furthermore, the conductive member 110 mayalso be a part of such a single-piece body.

On both sides of the waveguide member 122, the space between the surface125 of each stretch of artificial magnetic conductor and the conductivesurface 110 a of the conductive member 110 does not allow anelectromagnetic wave of any frequency that is within a specificfrequency band to propagate. This frequency band is called a “prohibitedband”. The artificial magnetic conductor is designed so that thefrequency of an electromagnetic wave (which hereinafter may be referredto as a signal wave) to propagate in the waveguide device 100 (which mayhereinafter be referred to as the “operating frequency”) is contained inthe prohibited band. The prohibited band may be adjusted based on thefollowing: the height of the conductive rods 124, i.e., the depth ofeach groove formed between adjacent conductive rods 124; the width ofeach conductive rod 124; the interval between conductive rods 124; andthe size of the gap between the leading end 124 a and the conductivesurface 110 a of each conductive rod 124.

Next, with reference to FIG. 4, the dimensions, shape, positioning, andthe like of each member will be described.

FIG. 4 is a diagram showing an exemplary range of dimension of eachmember in the structure shown in FIG. 2A. In the present specification,λo denotes a representative value of wavelengths in free space (e.g., acentral wavelength corresponding to a center frequency in the operatingfrequency band) of an electromagnetic wave (signal wave) propagating ina waveguide extending between the conductive surface 110 a of theconductive member 110 and the waveguide face 122 a of the waveguidemember 122. Moreover, λm denotes a wavelength, in free space, of anelectromagnetic wave of the highest frequency in the operating frequencyband. The end of each conductive rod 124 that is in contact with theconductive member 120 is referred to as the “root”. As shown in FIG. 4,each conductive rod 124 has the leading end 124 a and the root 124 b.Examples of dimensions, shapes, positioning, and the like of therespective members are as follows.

(1) Width of the Conductive Rod

The width (i.e., the size along the X direction and the Y direction) ofthe conductive rod 124 may be set to less than λm/2. Within this range,resonance of the lowest order can be prevented from occurring along theX direction and the Y direction. Since resonance may possibly occur notonly in the X and Y directions but also in any diagonal direction in anX-Y cross section, the diagonal length of an X-Y cross section of theconductive rod 124 is also preferably less than λm/2. The lower limitvalues for the rod width and diagonal length will conform to the minimumlengths that are producible under the given manufacturing method, but isnot particularly limited.

(2) Distance from the Root of the Conductive Rod to the ConductiveSurface of the Conductive Member 110

The distance from the root 124 b of each conductive rod 124 to theconductive surface 110 a of the conductive member 110 may be longer thanthe height of the conductive rods 124, while also being less than λm/2.When the distance is λm/2 or more, resonance may occur between the root124 b of each conductive rod 124 and the conductive surface 110 a, thusreducing the effect of signal wave containment.

The distance from the root 124 b of each conductive rod 124 to theconductive surface 110 a of the conductive members 110 corresponds tothe spacing between the conductive member 110 and the conductive member120. For example, when a signal wave of 76.5±0.5 GHz (which belongs tothe millimeter band or the extremely high frequency band) propagates inthe waveguide, the wavelength of the signal wave is in the range from3.8923 mm to 3.9435 mm. Therefore, λm equals 3.8923 mm in this case, sothat the spacing between the conductive member 110 and the conductivemember 120 may be set to less than a half of 3.8923 mm. So long as theconductive member 110 and the conductive member 120 realize such anarrow spacing while being disposed opposite from each other, theconductive member 110 and the conductive member 120 do not need to bestrictly parallel. Moreover, when the spacing between the conductivemember 110 and the conductive member 120 is less than λm/2, a whole or apart of the conductive member 110 and/or the conductive member 120 maybe shaped as a curved surface. On the other hand, the conductive members110 and 120 each have a planar shape (i.e., the shape of their region asperpendicularly projected onto the XY plane) and a planar size (i.e.,the size of their region as perpendicularly projected onto the XY plane)which may be arbitrarily designed depending on the purpose.

Although the conductive surface 120 a is illustrated as a plane in theexample shown in FIG. 2A, embodiments of the present disclosure are notlimited thereto. For example, as shown in FIG. 2B, the conductivesurface 120 a may be the bottom parts of faces each of which has a crosssection similar to a U-shape or a V-shape. The conductive surface 120 awill have such a structure when each conductive rod 124 or the waveguidemember 122 is shaped with a width which increases toward the root. Evenwith such a structure, the device shown in FIG. 2B can function as thewaveguide device according to an embodiment of the present disclosure solong as the distance between the conductive surface 110 a and theconductive surface 120 a is less than a half of the wavelength λm.

(3) Distance L2 from the Leading End of the Conductive Rod to theConductive Surface

The distance L2 from the leading end 124 a of each conductive rod 124 tothe conductive surface 110 a is set to less than λm/2. When the distanceis λm/2 or more, a propagation mode that reciprocates between theleading end 124 a of each conductive rod 124 and the conductive surface110 a may occur, thus no longer being able to contain an electromagneticwave. Note that, among the plurality of conductive rods 124, at leastthose which are adjacent to the waveguide member 122 do not have theirleading ends in electrical contact with the conductive surface 110 a. Asused herein, the leading end of a conductive rod not being in electricalcontact with the conductive surface means either of the followingstates: there being an air gap between the leading end and theconductive surface; or the leading end of the conductive rod and theconductive surface adjoining each other via an insulating layer whichmay exist in the leading end of the conductive rod or in the conductivesurface.

(4) Arrangement and Shape of Conductive Rods

The interspace between two adjacent conductive rods 124 among theplurality of conductive rods 124 has a width of less than λm/2, forexample. The width of the interspace between any two adjacent conductiverods 124 is defined by the shortest distance from the surface (sideface) of one of the two conductive rods 124 to the surface (side face)of the other. This width of the interspace between rods is to bedetermined so that resonance of the lowest order will not occur in theregions between rods. The conditions under which resonance will occurare determined based by a combination of: the height of the conductiverods 124; the distance between any two adjacent conductive rods; and thecapacitance of the air gap between the leading end 124 a of eachconductive rod 124 and the conductive surface 110 a. Therefore, thewidth of the interspace between rods may be appropriately determineddepending on other design parameters. Although there is no clear lowerlimit to the width of the interspace between rods, for manufacturingease, it may be e.g. λm/16 or more when an electromagnetic wave in theextremely high frequency range is to be propagated. Note that theinterspace does not need to have a constant width. So long as it remainsless than λm/2, the interspace between conductive rods 124 may vary.

The arrangement of the plurality of conductive rods 124 is not limitedto the illustrated example, so long as it exhibits a function of anartificial magnetic conductor. The plurality of conductive rods 124 donot need to be arranged in orthogonal rows and columns; the rows andcolumns may be intersecting at angles other than 90 degrees. Theplurality of conductive rods 124 do not need to form a linear arrayalong rows or columns, but may be in a dispersed arrangement which doesnot present any straightforward regularity. The conductive rods 124 mayalso vary in shape and size depending on the position on the conductivemember 120.

The surface 125 of the artificial magnetic conductor that areconstituted by the leading ends 124 a of the plurality of conductiverods 124 does not need to be a strict plane, but may be a plane withminute rises and falls, or even a curved surface. In other words, theconductive rods 124 do not need to be of uniform height, but rather theconductive rods 124 may be diverse so long as the array of conductiverods 124 is able to function as an artificial magnetic conductor.

Furthermore, each conductive rod 124 does not need to have a prismaticshape as shown in the figure, but may have a cylindrical shape, forexample. Furthermore, each conductive rod 124 does not need to have asimple columnar shape. The artificial magnetic conductor may also berealized by any structure other than an array of conductive rods 124,and various artificial magnetic conductors are applicable to thewaveguide device of the present disclosure. Note that, when the leadingend 124 a of each conductive rod 124 has a prismatic shape, its diagonallength is preferably less than λm/2. When the leading end 124 a of eachconductive rod 124 is shaped as an ellipse, the length of its major axisis preferably less than λm/2. Even when the leading end 124 a has anyother shape, the dimension across it is preferably less than λm/2 evenat the longest position.

The height of each conductive rod 124, i.e., the length from the root124 b to the leading end 124 a, may be set to a value which is shorterthan the distance (i.e., less than λm/2) between the conductive surface110 a and the conductive surface 120 a, e.g., λo/4.

(5) Width of the Waveguide Face

The width of the waveguide face 122 a of the waveguide member 122, i.e.,the size of the waveguide face 122 a along a direction which isorthogonal to the direction that the waveguide member 122 extends, maybe set to less than λm/2 (e.g. λm/8). If the width of the waveguide face122 a is λm/2 or more, resonance will occur along the width direction,which will prevent any WRG from operating as a simple transmission line.

(6) Height of the Waveguide Member

The height (i.e., the size along the Z direction in the example shown inthe figure) of the waveguide member 122 is set to less than λm/2. Thereason is that, if the distance is λm/2 or more, the distance betweenthe root 124 b of each conductive rod 124 and the conductive surface 110a will be λm/2 or more. Similarly, the height of the conductive rods 124(especially those conductive rods 124 which are adjacent to thewaveguide member 122) is set to less than λm/2.

(7) Distance L1 Between the Waveguide Face and the Conductive Surface

The distance L1 between the waveguide face 122 a of the waveguide member122 and the conductive surface 110 a is set to less than λm/2. If thedistance is λm/2 or more, resonance will occur between the waveguideface 122 a and the conductive surface 110 a, which will preventfunctionality as a waveguide. In one example, the distance is λm/4 orless. In order to ensure manufacturing ease, when an electromagneticwave in the extremely high frequency range is to propagate, the distanceL1 is preferably λm/16 or more, for example.

The lower limit of the distance L1 between the conductive surface 110 aand the waveguide face 122 a and the lower limit of the distance L2between the conductive surface 110 a and the leading end 124 a of eachconductive rod 124 depends on the machining precision, and also on theprecision when assembling the two upper/lower conductive members 110 and120 so as to be apart by a constant distance. When a pressing techniqueor an injection technique is used, the practical lower limit of theaforementioned distance is about 50 micrometers (μm). In the case ofusing an MEMS (Micro-Electro-Mechanical System) technique to make aproduct in e.g. the terahertz range, the lower limit of theaforementioned distance is about 2 to about 3 μm.

In the waveguide device 100 of the above-described construction, asignal wave of the operating frequency is unable to propagate in thespace between the surface 125 of the artificial magnetic conductor andthe conductive surface 110 a of the conductive member 110, butpropagates in the space between the waveguide face 122 a of thewaveguide member 122 and the conductive surface 110 a of the conductivemember 110. Unlike in a hollow waveguide, the width of the waveguidemember 122 in such a waveguide structure does not need to be equal to orgreater than a half of the wavelength of the electromagnetic wave topropagate. Moreover, the conductive member 110 and the conductive member120 do not need to be interconnected by a metal wall that extends alongthe thickness direction (i.e., in parallel to the YZ plane).

FIG. 5A schematically shows an electromagnetic wave that propagates in anarrow space, i.e., a gap between the waveguide face 122 a of thewaveguide member 122 and the conductive surface 110 a of the conductivemember 110. Three arrows in FIG. 5A schematically indicate theorientation of an electric field of the propagating electromagneticwave. The electric field of the propagating electromagnetic wave isperpendicular to the conductive surface 110 a of the conductive member110 and to the waveguide face 122 a.

On both sides of the waveguide member 122, stretches of artificialmagnetic conductor that are created by the plurality of conductive rods124 are present. An electromagnetic wave propagates in the gap betweenthe waveguide face 122 a of the waveguide member 122 and the conductivesurface 110 a of the conductive member 110. FIG. 5A is schematic, anddoes not accurately represent the magnitude of an electromagnetic fieldto be actually created by the electromagnetic wave. A part of theelectromagnetic wave (electromagnetic field) propagating in the spaceover the waveguide face 122 a may have a lateral expanse, to the outside(i.e., toward where the artificial magnetic conductor exists) of thespace that is delineated by the width of the waveguide face 122 a. Inthis example, the electromagnetic wave propagates in a direction (Ydirection) which is perpendicular to the plane of FIG. 5A. As such, thewaveguide member 122 does not need to extend linearly along the Ydirection, but may include a bend(s) and/or a branching portion(s) notshown. Since the electromagnetic wave propagates along the waveguideface 122 a of the waveguide member 122, the direction of propagationwould change at a bend, whereas the direction of propagation wouldramify into plural directions at a branching portion.

In the waveguide structure of FIG. 5A, no metal wall (electric wall),which would be indispensable to a hollow waveguide, exists on both sidesof the propagating electromagnetic wave. Therefore, in the waveguidestructure of this example, “a constraint due to a metal wall (electricwall)” is not included in the boundary conditions for theelectromagnetic field mode to be created by the propagatingelectromagnetic wave, and the width (size along the X direction) of thewaveguide face 122 a is less than a half of the wavelength of theelectromagnetic wave.

For reference, FIG. 5B schematically shows a cross section of a hollowwaveguide 130. With arrows, FIG. 5B schematically shows the orientationof an electric field of an electromagnetic field mode (TE₁₀) that iscreated in the internal space 132 of the hollow waveguide 130. Thelengths of the arrows correspond to electric field intensities. Thewidth of the internal space 132 of the hollow waveguide 130 needs to beset to be broader than a half of the wavelength. In other words, thewidth of the internal space 132 of the hollow waveguide 130 cannot beset to be smaller than a half of the wavelength of the propagatingelectromagnetic wave.

FIG. 5C is a cross-sectional view showing an implementation where twowaveguide members 122 are proved on the conductive member 120. Thus, anartificial magnetic conductor that is created by the plurality ofconductive rods 124 exists between the two adjacent waveguide members122. More accurately, stretches of artificial magnetic conductor createdby the plurality of conductive rods 124 are present on both sides ofeach waveguide member 122, such that each waveguide member 122 is ableto independently propagate an electromagnetic wave.

For reference's sake, FIG. 5D schematically shows a cross section of awaveguide device in which two hollow waveguides 130 are placedside-by-side. The two hollow waveguides 130 are electrically insulatedfrom each other. Each space in which an electromagnetic wave is topropagate needs to be surrounded by a metal wall that defines therespective hollow waveguide 130. Therefore, the interval between theinternal spaces 132 in which electromagnetic waves are to propagatecannot be made smaller than a total of the thicknesses of two metalwalls. Usually, a total of the thicknesses of two metal walls is longerthan a half of the wavelength of a propagating electromagnetic wave.Therefore, it is difficult for the interval between the hollowwaveguides 130 (i.e., interval between their centers) to be shorter thanthe wavelength of a propagating electromagnetic wave. Particularly forelectromagnetic waves of wavelengths in the extremely high frequencyrange (i.e., electromagnetic wave wavelength: 10 mm or less) or evenshorter wavelengths, a metal wall which is sufficiently thin relative tothe wavelength is difficult to be formed. This presents a cost problemin commercially practical implementation.

On the other hand, a waveguide device 100 including an artificialmagnetic conductor can easily realize a structure in which waveguidemembers 122 are placed close to one another. Thus, such a waveguidedevice 100 can be suitably used in an array antenna that includes pluralantenna elements in a close arrangement.

When a bend is to be provided in a waveguide member 122 of such awaveguide device in order to alter the direction of propagation ofsignal waves, it is necessary to suppress unwanted signal wavereflection. This requires an enhanced degree of impedance matching atthe bend. Structures based on a bent waveguide have long been used inmicrostrip lines, for example. In order to suppress reflection of signalwaves, it is considered preferable that the waveguide be gently bent;however, a broad space will be needed for accommodating a waveguidestructure which is bent in that manner. In order to efficiently disposea bent waveguide structure within a small space, it might be possible tobend the waveguide steeply (e.g., by 90°). In that case, however, it isgenerally practiced to cut off a portion of the corner in order tocounteract an increase in the waveguide width at the corner portion.

FIG. 6 is a diagram showing an exemplary construction in which an outercorner of a bend of a microstrip line is cut off. In the example shownin FIG. 6, in order to prevent the waveguide width d at the corner frombecoming larger than the waveguide width w at portions other than thecorner, the corner is partially (i.e., a portion indicated as x in thefigure) removed. This makes for an enhanced degree of matching, thussuppressing signal wave reflection.

A construction featuring such bends with truncated corners may similarlybe applied to the aforementioned ridge waveguide. An example of such astructure is disclosed in Non-Patent Document 2, for example.

FIG. 7 is a perspective view showing the structure of a ridge waveguidewhich is disclosed in Non-Patent Document 2. In this ridge waveguide,each bend of the ridge serving as a waveguide member is chamfered at itsouter corner. This construction is considered to be an application ofthe corner portion structure for microstrip lines as shown in FIG. 6 toa ridge waveguide.

However, it has been found through a study by the inventors that theconstruction shown in FIG. 7 cannot sufficiently suppress signal wavereflection. Hereinafter, this problem will be described with referenceto FIG. 8A through FIG. 8C.

FIG. 8A is a perspective view schematically showing a partialconstruction of a waveguide device according to Comparative Example.FIG. 8A shows a partial construction of a second conductive member 120,and a waveguide member 122 and electrically conductive rods 124 thereon.The aforementioned first conductive member 110 exists above theseconstituent elements. The waveguide member 122 has a bend 136 at which achange occurs in the direction that the waveguide member 122 extends.

For the sake of explanation, FIG. 8B illustrates the construction ofFIG. 8A with the conductive rods 124 removed therefrom. In such aconstruction of Comparative Example, signal wave reflection cannot besufficiently suppressed at the bend 136. The inventors have ascribed thecause of this to capacitive coupling that is occurring on the inside ofthe bend 136, which results in an excess capacitance component.

FIG. 8C is a diagram showing an equivalent circuit of the waveguidestructure of FIG. 8A. On the inside of the bend 136,electrically-conductive side faces of the waveguide member 122 lie closeto each other, thus allowing capacitive coupling therebetween.Consequently, as shown in FIG. 8C, an excess capacitance component C isadded at the position of the bend 136. It is considered that thiscapacitance component C causes the impedance at the bend 136 to changefrom the impedance of the case where there exists no bend 136, thusinducing unwanted reflection.

As will be described below in detail, the inventors have succeeded infurther enhancing the degree of impedance matching at a bend(s) byimproving the structure of the waveguide face or conductive surfacewhich pertains to the bend(s). With an enhanced degree of impedancematching, a waveguide device having an improved propagation efficiencyand less noise can be provided. It also allows to enhance theperformance of an antenna device that includes such a waveguide device.For example, signal wave reflection is reduced through impedancematching, whereby power loss can be reduced, and furthermore, disorderin the phase of the electromagnetic wave to propagate can be reduced.Therefore, in communications, deteriorations in a communication signalcan be suppressed; in a radar, precision of distance ordirection-of-arrival estimation can be improved.

Hereinafter, more specific exemplary constructions for waveguide devicesand antenna devices according to embodiments of the present disclosurewill be described. Note however that unnecessarily detailed descriptionsmay be omitted. For example, detailed descriptions on what is well knownin the art or redundant descriptions on what is substantially the sameconstitution may be omitted. This is to avoid lengthy description, andfacilitate the understanding of those skilled in the art. Theaccompanying drawings and the following description, which are providedby the inventors so that those skilled in the art can sufficientlyunderstand the present disclosure, are not intended to limit the scopeof claims.

<Waveguide Device>

Embodiment 1

FIG. 9A is a perspective view schematically showing a partial structureof a waveguide device according to Embodiment 1. FIG. 9B is an upperplan view of the structure of FIG. 9A as viewed from the Z direction.FIG. 9A and FIG. 9B only illustrate a portion close to a bend 136 of awaveguide member 122 as an example. In actuality, the conductive member120, the waveguide member 122, and the conductive rods 124 also exist inportions around that which is shown in the figure. This waveguide devicefurther includes a conductive member 110 (see FIG. 1 and the like) whichcovers over the waveguide member 122 and the conductive rods 124.

The waveguide member 122 includes a first portion 122A which extendsalong a first direction (which is the Y direction in the example of FIG.9A), a second portion 122B which extends along a second direction (whichis the X direction in the example of FIG. 9A), and a bend 136 thatconnects them. In this example, the direction that the waveguide member122 extends undergoes a 90° change at the bend 136. This angle does notneed to be 90° so long as the first direction and the second directionintersect each other. At the bend 136, the waveguide member 122 has arecess 137 made in the waveguide face 122 a.

The waveguide member 122 has a waveguide face 122 a presenting a stripeshape (which may also be referred to a “strip shape”), the waveguideface 122 a opposing the conductive surface 110 a of the conductivemember 110. In the present specification, a “stripe shape” means a shapewhich is defined by a single stripe, rather than a shape constituted bystripes. Not only shapes that extend linearly in one direction, but alsoany shape that bends or branches along the way is also encompassed by a“stripe shape”. In the case where any portion that undergoes a change inheight or width is provided on the waveguide face 122 a, it still fallsunder the meaning of “stripe shape” so long as the shape includes aportion that extends in one direction as viewed from the normaldirection of the waveguide face 122 a. A “stripe shape” may also bereferred to a “strip shape”.

In the present embodiment, a waveguide which is defined by theelectrically conductive surface 110 a of the conductive member 110, thewaveguide face 122 a of the waveguide member 122, and the plurality ofconductive rods 124 (artificial magnetic conductor) includes a gapenlargement, at which the gap between the conductive surface 110 a andthe waveguide face 122 a is locally increased. The gap enlargement inthe present embodiment is embodied by the recess 137 which is made inthe bend 136 of the waveguide member 122.

FIG. 9C is a diagram showing the structure of FIG. 9A with theconductive rods 124 removed therefrom, for illustration ease. Thewaveguide member 122 has electrically-conductive side faces 122 b whichconnect to the waveguide face 122 a. Although the recess 137 in thepresent embodiment is made across the entire bend 136, it suffices ifthe recess 137 has at least a partial overlap with the bend 136. In thepresent embodiment, the recess 137 reaches the side faces 122 b that areon the inside (i.e., lower side in the figure) of the bend 136 of thewaveguide member 122. Therefore, the height of the side faces 122 b onthe inside of the bend 136 is relatively low where the recess 137exists, while being relatively high in places other than the recess 137.In other words, the height h2 shown in FIG. 9C is smaller than theheight h1.

According to the present embodiment, the height of the waveguide member122 is lower at the bend 136, thus resulting in a greater spacingbetween the first conductive member 110 and the waveguide member 122.Such a structure provides a similar effect to introducing an inductancecomponent which is in series with the ridge waveguide (WRG).

FIG. 9D is a diagram showing an equivalent circuit of the ridgewaveguide of FIG. 9A. In the present embodiment, the recess 137 beingmade in the bend 136 enlarges the gap between the waveguide face 122 aand the conductive surface 110 a at the bend 136. This structure isequivalent to a structure where an inductance component L1 is added inseries to the ridge waveguide (i.e., in parallel to the capacitancecomponent C). As a result, a capacitance component C that has occurreddue to bending can be cancelled out with the inductance component L1. Asthe shape, size, position, and depth (i.e., difference between h1 and h2in FIG. 9C) of the recess 137 change, the values of the inductancecomponent L1 and the capacitance component C may also change. Therefore,the shape, size, position, and depth of the recess 137 may be designedso that the inductance component L1 and the capacitance component Ccancel out each other.

With the above construction, impedance matching at the bend 136 isensured; signal wave reflection is suppressed; and deteriorations intransmission efficiency can be suppressed.

Embodiment 2

FIG. 10A is a perspective view showing a partial structure of awaveguide device according to Embodiment 2. FIG. 10B is an upper planview of the structure of FIG. 10A as viewed from the Z direction. Thepresent embodiment differs from Embodiment 1 in that the outer corner ofthe bend 136 is chamfered. In addition to lowering the height of thewaveguide member 122 at the bend 136, the width is also narrowed toreduce the area in which the waveguide member 122 opposes the firstconductive member 110. This provides a similar effect to introducing aninductance component which is in series with the ridge waveguide,thereby further facilitating impedance matching.

FIG. 10C shows the structure of FIG. 10A with the conductive rods 124removed therefrom. The waveguide member 122 has a portion on the outsideof the bend 136 where the corner is chamfered (referred to as achamfered portion 138). The chamfered portion 138 is a portion thatremains after at least a portion of the outer corner of the bend 136 isremoved, and is partly or entirely flat. Instead of a structureresulting from chamfering the corner with a plane, a structure whichresults from chamfering the corner with a curved surface may be adopted.

FIG. 10D is a diagram showing enlarged a construction near a bend 136 ofa waveguide member 122. The first portion 122A and the second portion122B of the waveguide member 122 are physically and electricallyconnected via the bend 136. The first portion 122A extends along a firstdirection (which in this example is the Y direction), whereas the secondportion 122B extends along a second direction (which in this example isthe X direction) intersecting the first direction. The edge (or edges onboth sides) of the waveguide face 122 a according to the presentembodiment extends along the first direction in the first portion 122A,and along the second direction in the second portion 122B. At the bend136, the edge of the waveguide face 122 a includes transitory portions139A and 139B that each extend along a direction which is intermediatebetween the first direction and the second direction. The angleconstituted between the direction that the transitory portions 139A and139B extend (i.e., the direction extending from the closest point to thefirst portion 122A toward the closest point to the second portion 122Bin the transitory portions 139A and 139B) and the first direction issmaller than the angle which is constituted between the second directionand the first direction. In the example shown in the figure, thedirection that the angle constituted between the transitory portions139A and 139B extend and the first direction is about 45°, whereas theangle constituted between the second direction and the first directionis about 90°; however, this example is not a limitation. Note that thetransitory portions 139A and 139B do not need to be linear, but mayinclude a curved portion.

In the present embodiment, the length of the transitory portion 139B onthe inside of the bend 136 is shorter than the length of the transitoryportion 139A on the outside of the bend 136. The transitory portion 139Bon the inside of the bend 136 may have zero (0) length. In the presentembodiment, the upper edge of the chamfered portion 138 is flush withthe transitory portion 139A on the outside of the bend 136. One end 139a and the other end 139 b of the transitory portion 139A on the outsideof the bend 136 are located inside the gap enlargement (i.e., the recess137 shown hatched in FIG. 10D).

In the example shown in FIG. 10D, the width d2 of the waveguide face 122a at the bend 136 is similar to the width d1 of the waveguide face 122 ain any other portion; however, this example is not a limitation. Thechamfered portion 138 may be provided so that d2<d1, or d2>d1. Note thatthe chamfered portion 138 does not need to reach the root of thewaveguide member 122. The effect of the present embodiment can beobtained so long as the upper corner near the waveguide face 122 a ischamfered.

FIG. 10E and FIG. 10F are diagrams showing other exemplary constructionsfor a bend 136 of a waveguide member 122. In the example of FIG. 10E,the transitory portion 139A and the transitory portion 139B each have anarcuate shape. The radius of curvature of the transitory portion 139A isgreater than the radius of curvature of the transitory portion 139B. Thewidth d2 of the waveguide face 122 a at the bend 136 is narrower thanthe width d1 of the waveguide face 122 a at any other portion. In theexample of FIG. 10F, one end 139 a and the other end 139 b of thetransitory portion 139A each have an arcuate shape. In this example, thewidth d2 of the waveguide face 122 a at the bend 136 is substantiallyequal to the width d1 of the waveguide face 122 a at any other portion.In the example of FIG. 10F, while preventing an increase in the width ofthe waveguide face 122 a at the bend 136, the recess 137 is provided toensure impedance matching. In the example of FIG. 10E, while providingthe recess 137, a structure of intentionally narrowing the width of thewaveguide face 122 a at the bend 136 is adopted to achieve impedancematching.

FIG. 10G is a diagram showing an equivalent circuit of the ridgewaveguide of FIG. 10A. In the present embodiment, as compared to theconstruction of Embodiment 1, the width of the waveguide member 122 atthe bend 136 is narrow, and the area of the waveguide face 122 a at thebend 136 is small. This structure is equivalent to a structure in whichan inductance component L2 is added in series to the ridge waveguide(i.e., in parallel to the capacitance component C). As a result, thecapacitance component C occurring due to bending can be cancelled outwith not only the inductance component L1 but also the inductancecomponent L2. As the size of the portion to be chamfered in thewaveguide face 122 a changes, the size of the inductance component L2changes. Therefore, the size of the portion to be chamfered in thewaveguide face 122 a is to be designed so that the inductance componentL1 and the inductance component L2 cancel out the capacitance componentC.

With the above construction, impedance matching at the bend 136 isensured; signal wave reflection is suppressed; and deteriorations intransmission efficiency can be suppressed.

According to the present embodiment, inductance components can be addedto the bend 136 in two ways, thereby facilitating matching relative tothe construction of Embodiment 1. In particular, this facilitatesmatching across a broad frequency band, which will be required in thecase of handling radio waves of the UWB (Ultra Wide Band), for which alicense is not a requisite.

Hereinafter, with reference to FIG. 11, it will be described how theconstruction of the present embodiment provides an improved degree ofimpedance matching at the bend 136 of the waveguide member 122.

The inventors have made it clear through a simulation that theconstruction according to the present embodiment provides an improveddegree of impedance matching over the construction of ComparativeExample which lacks gap enlargement. Herein, the degree of impedancematching is represented by an input reflection coefficient. The inputreflection coefficient is a coefficient which represents a ratio of theintensity of a reflected wave to the intensity of an input wave, andrepresents the magnitude of return loss. It can be said that, the lowerthe input reflection coefficient is, the higher the degree of impedancematching is.

In this simulation, with respect to the constructions of ComparativeExample and Embodiment 2, an input reflection coefficient S in the casewhere an electromagnetic wave was allowed to propagate toward the bend136, while setting various parameters to appropriate values, wasmeasured.

FIG. 11 is a graph showing the results of this simulation. The graph ofFIG. 11 illustrates frequency dependence of the input reflectioncoefficient (unit: dB) with respect to each of Comparative Example andEmbodiment 2. As can be seen from FIG. 11, at any frequency, the returnloss is kept lower than in the construction of Comparative Example.Moreover, a return loss as low as −25 dB or less is achieved across abroad frequency range from 67 GHz to 85 GHz. In UWB, for which a licenseis not a requisite, a bandwidth accounting for 5% of the used frequencyis supposed to be required. It has been confirmed that the constructionaccording to the present embodiment achieves low losses across abandwidth which is far greater than this bandwidth.

(Variants)

Without being limited to the above embodiments, the waveguide deviceaccording to the present disclosure permits various modifications.Hereinafter, variants of the waveguide device will be described.

FIG. 12A is a diagram showing a first variant of a structure near a bend136 of a waveguide member 122. In this example, the waveguide member 122has no chamfered portion, and a recess 137 (hatched portion in thefigure) is formed in a region which is broader than the bend 136.

FIG. 12B is a diagram showing a second variant of a structure near abend 136 of a waveguide member 122. In this example, the bend 136 ischamfered on its outside, and a transitory portion 139A exists, but notransitory portion exists on the inside of the bend 136.

FIG. 12C is a diagram showing a third variant of a structure near a bend136 of a waveguide member 122. In this example, similarly to Embodiment2, the bend 136 is chamfered on its outside, and transitory portions139A and 139B respectively exist on the outside and the inside. A recess137 is formed over the entire bend 136. In this example, ends of thetransitory portions 139A and 139B are at ends of the bend 136.

FIG. 12D is a diagram showing a fourth variant of a structure near abend 136 of a waveguide member 122. In this example, only a portion ofthe bend 136 has an overlap with the recess 137 (gap enlargement). Therecess 137 reaches the side faces on the outside and on the inside ofthe bend 136. In this example, both ends of the transitory portion 139Aon the outside are at the outside of the gap enlargement (recess 137).

FIG. 12E is a diagram showing a fifth variant of a structure near a bend136 of a waveguide member 122. In this example, no transitory portionexists on the inside of the bend 136, but the recess 137 reaches theelectrically-conductive side faces 122 b on the inside of the bend 136.Although a transitory portion 139A exists on the outside of the bend136, the recess 137 does not reach the electrically-conductive sidefaces 122 c on the outside of the bend 136. With such a structure, too,an effect of introducing an inductance component to the bend 136 isobtained, thereby achieving an improved degree of impedance matching.

Note that, in any of the constructions of FIG. 12B through FIG. 12E, aconstruction where the outer corner of the bend 136 is not chamfered mayalso be adopted. Moreover, the chamfered portion does not need to reachthe root of the waveguide member 122.

FIG. 13 is a perspective view schematically showing another variant ofthe waveguide device. For convenience of explanation, FIG. 13illustrates the first conductive member 110 as being below the secondconductive member 120. Moreover, the waveguide member 122 hidden underthe conductive member 120 is indicated by a dotted line. In thisexample, a gap enlargement is realized not by the waveguide member 122,but by a recess 137A in the conductive member 110. The recess 137A ismade at a position opposing at least a portion of the bend 136 of thewaveguide member 122. The gap enlargement which is realized by therecess 137A may have an overlap with the entire bend 136, or have anoverlap with a part of the bend 136. In addition to such a recess 137A,a recess may also be made in the bend 136 of the waveguide member 122.Thus, the gap enlargement according to the present disclosure isrealized by a recess(s) made in at least one of the waveguide member 122and the conductive member 110.

The waveguide member 122 may include an impedance transformer at aportion adjacent to the bend 136. Given a wavelength λr of anelectromagnetic wave having the center frequency, within the waveguide,of the operating frequency band of the waveguide device, an impedancetransformer can be implemented by a bump which is provided in a regionadjacent to the bend 136 which is λr/4 long. A plurality of such bumpsmay be provided so as to have a different height for every length ofλr/4. Instead of bumps, broad portions may be utilized as impedancetransformers.

Next, other variants of the waveguide member 122, the conductive members110 and 120, and the conductive rod 124 will be described.

FIG. 14A is a cross-sectional view showing an exemplary structure inwhich only the waveguide face 122 a, defining an upper face of thewaveguide member 122, is electrically conductive, while any portion ofthe waveguide member 122 other than the waveguide face 122 a is notelectrically conductive. Both of the first conductive member 110 and thesecond conductive member 120 alike are only electrically conductive attheir surface that has the waveguide member 122 provided thereon (i.e.,the conductive surface 110 a, 120 a), while not being electricallyconductive in any other portions. Thus, each of the waveguide member122, the first conductive member 110, and the second conductive member120 does not need to be electrically conductive.

FIG. 14B is a diagram showing a variant in which the waveguide member122 is not formed on the second conductive member 120. In this example,the waveguide member 122 is fixed to a supporting member (e.g., an outerperipheral wall of the housing) that supports the first conductivemember 110 and the second conductive member. A gap exists between thewaveguide member 122 and the second conductive member 120. Thus, thewaveguide member 122 does not need to be connected to the secondconductive member 120.

FIG. 14C is a diagram showing an exemplary structure where the secondconductive member 120, the waveguide member 122, and each of theplurality of conductive rods 124 are composed of a dielectric surfacethat is coated with an electrically conductive material such as a metal.The second conductive member 120, the waveguide member 122, and theplurality of conductive rods 124 are connected to one another via theelectrical conductor. On the other hand, the first conductive member 110is made of an electrically conductive material such as a metal.

FIG. 14D and FIG. 14E are diagrams each showing an exemplary structurein which dielectric layers 110 b and 120 b are respectively provided onthe outermost surfaces of conductive members 110 and 120, a waveguidemember 122, and conductive rods 124. FIG. 14D shows an exemplarystructure in which the surface of metal conductive members, which areconductors, are covered with a dielectric layer. FIG. 14E shows anexample where the conductive member 120 is structured so that thesurface of members which are composed of a dielectric, e.g., resin, iscovered with a conductor such as a metal, this metal layer being furthercoated with a dielectric layer. The dielectric layer that covers themetal surface may be a coating of resin or the like, or an oxide film ofpassivation coating or the like which is generated as the metal becomesoxidized.

The dielectric layer on the outermost surface will allow losses to beincreased in the electromagnetic wave propagating through the WRGwaveguide, but is able to protect the conductive surfaces 110 a and 120a (which are electrically conductive) from corrosion. It also preventsinfluences of a DC voltage, or an AC voltage of such a low frequencythat it is not capable of propagation on certain WRG waveguides.

FIG. 14F is a diagram showing an example where the height of thewaveguide member 122 is lower than the height of the conductive rods124, and the conductive surface 110 a of the first conductive member 110protrudes toward the waveguide member 122. Even such a structure willoperate in a similar manner to the above-described embodiment, so longas the ranges of dimensions depicted in FIG. 4 are satisfied.

FIG. 14G is a diagram showing an example where, further in the structureof FIG. 14F, portions of the conductive surface 110 a that oppose theconductive rods 124 protrude toward the conductive rods 124. Even such astructure will operate in a similar manner to the above-describedembodiment, so long as the ranges of dimensions depicted in FIG. 4 aresatisfied. Instead of a structure in which the conductive surface 110 apartially protrudes, a structure in which the conductive surface 110 ais partially dented may be adopted.

FIG. 15A is a diagram showing an example where a conductive surface 110a of the first conductive member 110 is shaped as a curved surface. FIG.15B is a diagram showing an example where also a conductive surface 120a of the second conductive member 120 is shaped as a curved surface. Asdemonstrated by these examples, at least one of the conductivesurface(s) 110 a, 120 a may not be shaped as a plane(s), but may beshaped as a curved surface(s). In particular, as has been described withreference to FIG. 2B, the second conductive member 120 may have aconductive surface 120 a which, macroscopically, lacks any planarportion.

<Antenna Device>

Next, an illustrative embodiment of an antenna device including awaveguide device according to the present disclosure will be described.

An antenna device according to the present embodiment includes awaveguide device according to any of the above-described embodiments,and at least one antenna element which is connected to the waveguidedevice. The antenna element has at least one of: a function of radiatinginto space an electromagnetic wave which has propagated through awaveguide in the waveguide device; and a function of introducing anelectromagnetic wave which has propagated through space to a waveguidein the waveguide device. In other words, the antenna device according tothe present embodiment is used for at least one of signal transmissionand signal reception.

FIG. 16A is an upper plan view of an antenna device (array antenna)including 16 slots (openings) 112 in an array of 4 rows and 4 columns,as viewed from the Z direction. FIG. 16B is a cross-sectional view takenalong line B-B in FIG. 16A. In the antenna device shown in the figures,a first waveguide device 100 a and a second waveguide device 100 b arelayered. The first waveguide device 100 a includes waveguide members122U that directly couple to slots 112 functioning as radiation elements(antenna elements). The second waveguide device 100 b includes furtherwaveguide members 122L that couple to the waveguide members 122U of thefirst waveguide device 100 a. The waveguide members 122L and theconductive rods 124L of the second waveguide device 100 b are arrangedon a third conductive member 140. The second waveguide device 100 b isbasically similar in construction to the first waveguide device 100 a.

On the first conductive member 110 in the first waveguide device 100 a,side walls 114 surrounding each slot 112 are provided. The side walls114 form a horn that adjusts directivity of the slot 112. The number andarrangement of slots 112 in this example are only illustrative. Theorientations and shapes of the slots 112 are not limited to those of theexample shown in the figures, either. It is not intended that theexample shown in the figures provides any limitation as to whether theside walls 114 of each horn are tilted or not, the angles thereof, orthe shape of each horn.

FIG. 17A is a diagram showing a planar layout of waveguide members 122Uin the first waveguide device 100 a. FIG. 17B is a diagram showing aplanar layout of a waveguide member 122L in the second waveguide device100 b. As is clear from these figures, the waveguide members 122U of thefirst waveguide device 100 a extend linearly, and include no branchingportions or bends; on the other hand, the waveguide members 122L of thesecond waveguide device 100 b include both branching portions and bends.In terms of fundamental construction of the waveguide device, thecombination of the “second conductive member 120” and the “thirdconductive member 140” in the second waveguide device 100 b correspondsto the combination in the first waveguide device 100 a of the “firstconductive member 110” and the “second conductive member 120”.

What is characteristic in the array antenna shown in the figures is thata recess is formed in each of six bends 136 which the waveguide member122L has. As a result, the degree of impedance matching is improved atthe bends 136 of the waveguide members 122L.

The waveguide members 122U of the first waveguide device 100 a couple tothe waveguide member 122L of the second waveguide device 100 b, throughports (openings) 145U that are provided in the second conductive member120. Stated otherwise, an electromagnetic wave which has propagatedthrough the waveguide member 122L of the second waveguide device 100 bpasses through a port 145U to reach a waveguide member 122U of the firstwaveguide device 100 a, and propagates through the waveguide member 122Uof the first waveguide device 100 a. In this case, each slot 112functions as an antenna element to allow an electromagnetic wave whichhas propagated through the waveguide to be emitted into space.Conversely, when an electromagnetic wave which has propagated in spaceimpinges on a slot 112, the electromagnetic wave couples to thewaveguide member 122U of the first waveguide device 100 a that liesdirectly under that slot 112, and propagates through the waveguidemember 122U of the first waveguide device 100 a. An electromagnetic wavewhich has propagated through a waveguide member 122U of the firstwaveguide device 100 a may also pass through a port 145U to reach thewaveguide member 122L of the second waveguide device 100 b, andpropagates through the waveguide member 122L of the second waveguidedevice 100 b. Via a port 145L of the third conductive member 140, thewaveguide member 122L of the second waveguide device 100 b may couple toan external waveguide device or radio frequency circuit (electroniccircuit). As one example, FIG. 17B illustrates an electronic circuit 200which is connected to the port 145L. Without being limited to a specificposition, the electronic circuit 200 may be provided at any arbitraryposition. The electronic circuit 200 may be provided on a circuit boardwhich is on the rear surface side (i.e., the lower side in FIG. 16B) ofthe third conductive member 140, for example. Such an electronic circuitis a microwave integrated circuit, which may be an MMIC (MonolithicMicrowave Integrated Circuit) that generates or receives millimeterwaves, for example.

The first conductive member 110 shown in FIG. 16A may be called an“emission layer”. Moreover, the entirety of the second conductive member120, the waveguide members 122U, and the conductive rods 124U shown inFIG. 17A may be called an “excitation layer”, whereas the entirety ofthe third conductive member 140, the waveguide member 122L, and theconductive rods 124L shown in FIG. 17B may be called a “distributionlayer”. Moreover, the “excitation layer” and the “distribution layer”may be collectively called a “feeding layer”. Each of the “emissionlayer”, the “excitation layer”, and the “distribution layer” can bemass-produced by processing a single metal plate. The radiation layer,the excitation layer, the distribution layer, and the electroniccircuitry to be provided on the rear face side of the distribution layermay be fabricated as a single-module product.

In the array antenna of this example, as can be seen from FIG. 16B, anemission layer, an excitation layer, and a distribution layer arelayered, which are in plate form; therefore, a flat and low-profile flatpanel antenna is realized as a whole. For example, the height(thickness) of a multilayer structure having a cross-sectionalconstruction as shown in FIG. 16B can be set to 10 mm or less.

With the waveguide member 122L shown in FIG. 17B, the distances from theport 145L of the third conductive member 140 to the respective ports145U (see FIG. 17A) of the second conductive member 120 measured alongthe waveguide member 122L are all equal. Therefore, a signal wave whichis input to the waveguide member 122L reaches the four ports 145U of thesecond conductive member 120 all in the same phase, from the port 145Lof the third conductive member 140. As a result, the four waveguidemembers 122U on the second conductive member 120 can be excited in thesame phase.

It is not necessary for all slots 112 functioning as antenna elements toemit electromagnetic waves in the same phase. The network patterns ofthe waveguide members 122U and 122L in the excitation layer and thedistribution layer may be arbitrary, and they may be arranged so thatthe respective waveguide members 122U and 122L independently propagatedifferent signals.

Although the waveguide members 122U of the first waveguide device 100 ain this example include neither a branching portion nor a bend, thewaveguide device functioning as an excitation layer may also include awaveguide member having at least one of a branching portion and a bend.As mentioned earlier, it is not necessary for all conductive rods in thewaveguide device to be similar in shape.

The waveguide device and antenna device according to the presentembodiment can be suitably used in a radar device or a radar system tobe incorporated in moving entities such as vehicles, marine vessels,aircraft, robots, or the like, for example. A radar device would includean antenna device according to an embodiment of the present disclosureand a microwave integrated circuit that is connected to the antennadevice. A radar system would include the radar device and a signalprocessing circuit that is connected to the microwave integrated circuitof the radar device. An antenna device according to the presentembodiment includes a WRG structure which permits downsizing, and thusallows the area of the face on which antenna elements are arrayed to bereduced, as compared to a construction in which a conventional hollowwaveguide is used. Therefore, a radar system incorporating the antennadevice can be easily mounted in a narrow place such as a face of arearview mirror in a vehicle that is opposite to its specular surface,or a small-sized moving entity such as a UAV (an Unmanned AerialVehicle, a so-called drone). Note that, without being limited to theimplementation where it is mounted in a vehicle, a radar system may beused while being fixed on the road or a building, for example.

A slot array antenna according to an embodiment of the presentdisclosure can also be used in a wireless communication system. Such awireless communication system would include a slot array antennaaccording to any of the above embodiments and a communication circuit (atransmission circuit or a reception circuit). Details of exemplaryapplications to wireless communication systems will be described later.

A slot array antenna according to an embodiment of the presentdisclosure can further be used as an antenna in an indoor positioningsystem (IPS). An indoor positioning system is able to identify theposition of a moving entity, such as a person or an automated guidedvehicle (AGV), that is in a building. An array antenna can also be usedas a radio wave transmitter (beacon) for use in a system which providesinformation to an information terminal device (e.g., a smartphone) thatis carried by a person who has visited a store or any other facility. Insuch a system, once every several seconds, a beacon may radiate anelectromagnetic wave carrying an ID or other information superposedthereon, for example. When the information terminal device receives thiselectromagnetic wave, the information terminal device transmits thereceived information to a remote server computer via telecommunicationlines. Based on the information that has been received from theinformation terminal device, the server computer identifies the positionof that information terminal device, and provides information which isassociated with that position (e.g., product information or a coupon) tothe information terminal device.

The present specification employs the term “artificial magneticconductor” in describing the technique according to the presentdisclosure, this being in line with what is set forth in a paper by oneof the inventors Kirino (Non-Patent Document 1) as well as a paper byKildal et al., who published a study directed to related subject matteraround the same time. However, it has been found through a study by theinventors that the invention according to the present disclosure doesnot necessarily require an “artificial magnetic conductor” under itsconventional definition. That is, while a periodic structure has beenbelieved to be a requirement for an artificial magnetic conductor, theinvention according to the present disclosure does not necessary requirea periodic structure in order to be practiced.

The artificial magnetic conductor that is described in the presentdisclosure consists of rows of conductive rods. In order to preventelectromagnetic waves from leaking away from the waveguide face, it hasbeen believed essential that there exist at least two rows of conductiverods on one side of the waveguide member(s), such rows of conductiverods extending along the waveguide member(s) (ridge(s)). The reason isthat it takes at least two rows of conductive rods for them to have a“period”. However, according to a study by the inventors, even when onlyone row of conductive rods, or only one conductive rod, exists betweentwo waveguide members that extend in parallel to each other, theintensity of a signal that leaks from one waveguide member to the otherwaveguide member can be suppressed to −10 dB or less, which is apractically sufficient value in many applications. The reason why such asufficient level of separation is achieved with only an imperfectperiodic structure is so far unclear. However, in view of this fact, inthe present disclosure, the conventional notion of “artificial magneticconductor” is extended so that the term also encompasses a structureincluding only one row of conductive rods, or only one conductive rod.

Application Example 1: Onboard Radar System

Next, as an Application Example of utilizing the above-described arrayantenna, an instance of an onboard radar system including an arrayantenna will be described. A transmission wave used in an onboard radarsystem may have a frequency of e.g. 76 gigahertz (GHz) band, which willhave a wavelength λo of about 4 mm in free space.

In safety technology of automobiles, e.g., collision avoidance systemsor automated driving, it is particularly essential to identify one ormore vehicles (targets) that are traveling ahead of the driver'svehicle. As a method of identifying vehicles, techniques of estimatingthe directions of arriving waves by using a radar system have been underdevelopment.

FIG. 18 shows a driver's vehicle 500, and a preceding vehicle 502 thatis traveling in the same lane as the driver's vehicle 500. The driver'svehicle 500 includes an onboard radar system which incorporates an arrayantenna according to the above-described embodiment. When the onboardradar system of the driver's vehicle 500 radiates a radio frequencytransmission signal, the transmission signal reaches the precedingvehicle 502 and is reflected therefrom, so that a part of the signalreturns to the driver's vehicle 500. The onboard radar system receivesthis signal to calculate a position of the preceding vehicle 502, adistance (“range”) to the preceding vehicle 502, velocity, etc.

FIG. 19 shows the onboard radar system 510 of the driver's vehicle 500.The onboard radar system 510 is provided within the vehicle. Morespecifically, the onboard radar system 510 is disposed on a face of therearview mirror that is opposite to its specular surface. From withinthe vehicle, the onboard radar system 510 radiates a radio frequencytransmission signal in the direction of travel of the vehicle 500, andreceives a signal(s) which arrives from the direction of travel.

The onboard radar system 510 of this Application Example includes a slotarray antenna according to the above embodiment. This ApplicationExample is arranged so that the direction that each of the plurality ofwaveguide members extends coincides with the vertical direction, andthat the direction in which the plurality of waveguide members arearrayed (with respect to one another) coincides with the horizontaldirection. As a result, the lateral dimension of the plurality of slotsas viewed from the front can be reduced. Exemplary dimensions of anantenna device including the above array antenna may be 60 mm (wide)×30mm (long)×10 mm (deep). It will be appreciated that this is a very smallsize for a millimeter wave radar system of the 76 GHz band.

Note that many a conventional onboard radar system is provided outsidethe vehicle, e.g., at the tip of the front nose. The reason is that theonboard radar system is relatively large in size, and thus is difficultto be provided within the vehicle as in the present disclosure. Theonboard radar system 510 of this Application Example may be installedwithin the vehicle as described above, but may instead be mounted at thetip of the front nose. Since the footprint of the onboard radar systemon the front nose is reduced, other parts can be more easily placed.

The Application Example allows the interval between a plurality ofwaveguide members (ridges) that are used in the transmission antenna tobe narrow, which also narrows the interval between a plurality of slotsto be provided opposite from a number of adjacent waveguide members.This reduces the influences of grating lobes. For example, when theinterval between the centers of two laterally adjacent slots is shorterthan the free-space wavelength λo of the transmission wave (i.e., lessthan about 4 mm), no grating lobes will occur frontward. As a result,influences of grating lobes are reduced. Note that grating lobes willoccur when the interval at which the antenna elements are arrayed isgreater than a half of the wavelength of an electromagnetic wave. If theinterval at which the antenna elements are arrayed is less than thewavelength, no grating lobes will occur frontward. Therefore, in thecase where each antenna element composing an array antenna is onlyfrontward-sensitive, as in the Application Example, grating lobes willexert substantially no influences so long as the interval at which theantenna elements are arrayed is smaller than the wavelength. Byadjusting the array factor of the transmission antenna, the directivityof the transmission antenna can be adjusted. A phase shifter may beprovided so as to be able to individually adjust the phases ofelectromagnetic waves that are transmitted on plural waveguide members.By providing a phase shifter, the directivity of the transmissionantenna can be changed in any desired direction. Since the constructionof a phase shifter is well-known, description thereof will be omitted.

A reception antenna according to the Application Example is able toreduce reception of reflected waves associated with grating lobes,thereby being able to improve the precision of the below-describedprocessing. Hereinafter, an example of a reception process will bedescribed.

FIG. 20A shows a relationship between an array antenna AA of the onboardradar system 510 and plural arriving waves k (k: an integer from 1 to K;the same will always apply below. K is the number of targets that arepresent in different azimuths). The array antenna AA includes M antennaelements in a linear array. Principlewise, an antenna can be used forboth transmission and reception, and therefore the array antenna AA canbe used for both a transmission antenna and a reception antenna.Hereinafter, an example method of processing an arriving wave which isreceived by the reception antenna will be described.

The array antenna AA receives plural arriving waves that simultaneouslyimpinge at various angles. Some of the plural arriving waves may bearriving waves which have been radiated from the transmission antenna ofthe same onboard radar system 510 and reflected by a target(s).Furthermore, some of the plural arriving waves may be direct or indirectarriving waves that have been radiated from other vehicles.

The incident angle of each arriving wave (i.e., an angle representingits direction of arrival) is an angle with respect to the broadside B ofthe array antenna AA. The incident angle of an arriving wave representsan angle with respect to a direction which is perpendicular to thedirection of the line along which antenna elements are arrayed.

Now, consider a k^(th) arriving wave. Where K arriving waves areimpinging on the array antenna from K targets existing at differentazimuths, a “k^(th) arriving wave” means an arriving wave which isidentified by an incident angle θ_(k).

FIG. 20B shows the array antenna AA receiving the k^(th) arriving wave.The signals received by the array antenna AA can be expressed as a“vector” having M elements, by Math. 1.S=[s ₁ ,s ₂ , . . . ,s _(M)]^(T)  (Math. 1)

In the above, s_(m) (where m is an integer from 1 to M; the same willalso be true hereinbelow) is the value of a signal which is received byan m^(th) antenna element. The superscript^(T) means transposition. S isa column vector. The column vector S is defined by a product ofmultiplication between a direction vector (referred to as a steeringvector or a mode vector) as determined by the construction of the arrayantenna and a complex vector representing a signal from each target(also referred to as a wave source or a signal source). When the numberof wave sources is K, the waves of signals arriving at each individualantenna element from the respective K wave sources are linearlysuperposed. In this state, s_(m) can be expressed by Math. 2.

$\begin{matrix}{S_{m} = {\sum\limits_{k = 1}^{K}\;{a_{k}\mspace{11mu}\exp\left\{ {j\left( {{\frac{2\;\pi}{\lambda}d_{m}\sin\mspace{11mu}\theta_{k}} + \varphi_{k}} \right)} \right\}}}} & \left\lbrack {{Math}.\mspace{14mu} 2} \right\rbrack\end{matrix}$

In Math. 2, a_(k), θ_(k) and ϕ_(k) respectively denote the amplitude,incident angle, and initial phase of the k^(th) arriving wave. Moreover,λ denotes the wavelength of an arriving wave, and j is an imaginaryunit.

As will be understood from Math. 2, s_(m) is expressed as a complexnumber consisting of a real part (Re) and an imaginary part (Im).

When this is further generalized by taking noise (internal noise orthermal noise) into consideration, the array reception signal X can beexpressed as Math. 3.X=S+N  (Math. 3)

N is a vector expression of noise.

The signal processing circuit generates a spatial covariance matrix Rxx(Math. 4) of arriving waves by using the array reception signal Xexpressed by Math. 3, and further determines eigenvalues of the spatialcovariance matrix Rxx.

$\begin{matrix}\begin{matrix}{R_{xx} = {XX}^{H}} \\{= \begin{bmatrix}{R\;{xx}_{11}} & \ldots & {R\;{xx}_{1\; M}} \\\vdots & \ddots & \vdots \\{R\;{xx}_{M\; 1}} & \ldots & {R\;{xx}_{MM}}\end{bmatrix}}\end{matrix} & \left\lbrack {{Math}.\mspace{14mu} 4} \right\rbrack\end{matrix}$

In the above, the superscript^(H) means complex conjugate transposition(Hermitian conjugate).

Among the eigenvalues, the number of eigenvalues which have values equalto or greater than a predetermined value that is defined based onthermal noise (signal space eigenvalues) corresponds to the number ofarriving waves. Then, angles that produce the highest likelihood as tothe directions of arrival of reflected waves (i.e. maximum likelihood)are calculated, whereby the number of targets and the angles at whichthe respective targets are present can be identified. This process isknown as a maximum likelihood estimation technique.

Next, see FIG. 21. FIG. 21 is a block diagram showing an exemplaryfundamental construction of a vehicle travel controlling apparatus 600according to the present disclosure. The vehicle travel controllingapparatus 600 shown in FIG. 21 includes a radar system 510 which ismounted in a vehicle, and a travel assistance electronic controlapparatus 520 which is connected to the radar system 510. The radarsystem 510 includes an array antenna AA and a radar signal processingapparatus 530.

The array antenna AA includes a plurality of antenna elements, each ofwhich outputs a reception signal in response to one or plural arrivingwaves. As mentioned earlier, the array antenna AA is capable ofradiating a millimeter wave of a high frequency. Note that, withoutbeing limited to the array antenna according to the above embodiment,the array antenna AA may be any other array antenna that suitablyperforms reception.

In the radar system 510, the array antenna AA needs to be attached tothe vehicle, while at least some of the functions of the radar signalprocessing apparatus 530 may be implemented by a computer 550 and adatabase 552 which are provided externally to the vehicle travelcontrolling apparatus 600 (e.g., outside of the driver's vehicle). Inthat case, the portions of the radar signal processing apparatus 530that are located within the vehicle may be perpetually or occasionallyconnected to the computer 550 and database 552 external to the vehicleso that bidirectional communications of signal or data are possible. Thecommunications are to be performed via a communication device 540 of thevehicle and a commonly-available communications network.

The database 552 may store a program which defines various signalprocessing algorithms. The content of the data and program needed forthe operation of the radar system 510 may be externally updated via thecommunication device 540. Thus, at least some of the functions of theradar system 510 can be realized externally to the driver's vehicle(which is inclusive of the interior of another vehicle), by a cloudcomputing technique. Therefore, an “onboard” radar system in the meaningof the present disclosure does not require that all of its constituentelements be mounted within the (driver's) vehicle. However, forsimplicity, the present application will describe an implementation inwhich all constituent elements according to the present disclosure aremounted in a single vehicle (i.e., the driver's vehicle), unlessotherwise specified.

The radar signal processing apparatus 530 includes a signal processingcircuit 560. The signal processing circuit 560 directly or indirectlyreceives reception signals from the array antenna AA, and inputs thereception signals, or a secondary signal(s) which has been generatedfrom the reception signals, to an arriving wave estimation unit AU. Apart or a whole of the circuit (not shown) which generates a secondarysignal(s) from the reception signals does not need to be provided insideof the signal processing circuit 560. A part or a whole of such acircuit (preprocessing circuit) may be provided between the arrayantenna AA and the radar signal processing apparatus 530.

The signal processing circuit 560 is configured to perform computationby using the reception signals or secondary signal(s), and output asignal indicating the number of arriving waves. As used herein, a“signal indicating the number of arriving waves” can be said to be asignal indicating the number of preceding vehicles (which may be onepreceding vehicle or plural preceding vehicles) ahead of the driver'svehicle.

The signal processing circuit 560 may be configured to execute varioussignal processing which is executable by known radar signal processingapparatuses. For example, the signal processing circuit 560 may beconfigured to execute “super-resolution algorithms” such as the MUSICmethod, the ESPRIT method, or the SAGE method, or other algorithms fordirection-of-arrival estimation of relatively low resolution.

The arriving wave estimation unit AU shown in FIG. 21 estimates an anglerepresenting the azimuth of each arriving wave by an arbitrary algorithmfor direction-of-arrival estimation, and outputs a signal indicating theestimation result. The signal processing circuit 560 estimates thedistance to each target as a wave source of an arriving wave, therelative velocity of the target, and the azimuth of the target by usinga known algorithm which is executed by the arriving wave estimation unitAU, and output a signal indicating the estimation result.

In the present disclosure, the term “signal processing circuit” is notlimited to a single circuit, but encompasses any implementation in whicha combination of plural circuits is conceptually regarded as a singlefunctional part. The signal processing circuit 560 may be realized byone or more System-on-Chips (SoCs). For example, a part or a whole ofthe signal processing circuit 560 may be an FPGA (Field-ProgrammableGate Array), which is a programmable logic device (PLD). In that case,the signal processing circuit 560 includes a plurality of computationelements (e.g., general-purpose logics and multipliers) and a pluralityof memory elements (e.g., look-up tables or memory blocks).Alternatively, the signal processing circuit 560 may be a set of ageneral-purpose processor(s) and a main memory device(s). The signalprocessing circuit 560 may be a circuit which includes a processorcore(s) and a memory device(s). These may function as the signalprocessing circuit 560.

The travel assistance electronic control apparatus 520 is configured toprovide travel assistance for the vehicle based on various signals whichare output from the radar signal processing apparatus 530. The travelassistance electronic control apparatus 520 instructs various electroniccontrol units to fulfill predetermined functions, e.g., a function ofissuing an alarm to prompt the driver to make a braking operation whenthe distance to a preceding vehicle (vehicular gap) has become shorterthan a predefined value; a function of controlling the brakes; and afunction of controlling the accelerator. For example, in the case of anoperation mode which performs adaptive cruise control of the driver'svehicle, the travel assistance electronic control apparatus 520 sendspredetermined signals to various electronic control units (not shown)and actuators, to maintain the distance of the driver's vehicle to apreceding vehicle at a predefined value, or maintain the travelingvelocity of the driver's vehicle at a predefined value.

In the case of the MUSIC method, the signal processing circuit 560determines eigenvalues of the spatial covariance matrix, and, as asignal indicating the number of arriving waves, outputs a signalindicating the number of those eigenvalues (“signal space eigenvalues”)which are greater than a predetermined value (thermal noise power) thatis defined based on thermal noise.

Next, see FIG. 22. FIG. 22 is a block diagram showing another exemplaryconstruction for the vehicle travel controlling apparatus 600. The radarsystem 510 in the vehicle travel controlling apparatus 600 of FIG. 22includes an array antenna AA, which includes an array antenna that isdedicated to reception only (also referred to as a reception antenna) Rxand an array antenna that is dedicated to transmission only (alsoreferred to as a transmission antenna) Tx; and an object detectionapparatus 570.

At least one of the transmission antenna Tx and the reception antenna Rxhas the aforementioned waveguide structure. The transmission antenna Txradiates a transmission wave, which may be a millimeter wave, forexample. The reception antenna Rx that is dedicated to reception onlyoutputs a reception signal in response to one or plural arriving waves(e.g., a millimeter wave(s)).

A transmission/reception circuit 580 sends a transmission signal for atransmission wave to the transmission antenna Tx, and performs“preprocessing” for reception signals of reception waves received at thereception antenna Rx. A part or a whole of the preprocessing may beperformed by the signal processing circuit 560 in the radar signalprocessing apparatus 530. A typical example of preprocessing to beperformed by the transmission/reception circuit 580 may be generating abeat signal from a reception signal, and converting a reception signalof analog format into a reception signal of digital format.

Note that the radar system according to the present disclosure may,without being limited to the implementation where it is mounted in thedriver's vehicle, be used while being fixed on the road or a building.

Next, an example of a more specific construction of the vehicle travelcontrolling apparatus 600 will be described.

FIG. 23 is a block diagram showing an example of a more specificconstruction of the vehicle travel controlling apparatus 600. Thevehicle travel controlling apparatus 600 shown in FIG. 23 includes aradar system 510 and an onboard camera system 700. The radar system 510includes an array antenna AA, a transmission/reception circuit 580 whichis connected to the array antenna AA, and a signal processing circuit560.

The onboard camera system 700 includes an onboard camera 710 which ismounted in a vehicle, and an image processing circuit 720 whichprocesses an image or video that is acquired by the onboard camera 710.

The vehicle travel controlling apparatus 600 of this Application Exampleincludes an object detection apparatus 570 which is connected to thearray antenna AA and the onboard camera 710, and a travel assistanceelectronic control apparatus 520 which is connected to the objectdetection apparatus 570. The object detection apparatus 570 includes atransmission/reception circuit 580 and an image processing circuit 720,in addition to the above-described radar signal processing apparatus 530(including the signal processing circuit 560). The object detectionapparatus 570 detects a target on the road or near the road, by usingnot only the information which is obtained by the radar system 510 butalso the information which is obtained by the image processing circuit720. For example, while the driver's vehicle is traveling in one of twoor more lanes of the same direction, the image processing circuit 720can distinguish which lane the driver's vehicle is traveling in, andsupply that result of distinction to the signal processing circuit 560.When the number and azimuth(s) of preceding vehicles are to berecognized by using a predetermined algorithm for direction-of-arrivalestimation (e.g., the MUSIC method), the signal processing circuit 560is able to provide more reliable information concerning a spatialdistribution of preceding vehicles by referring to the information fromthe image processing circuit 720.

Note that the onboard camera system 700 is an example of a means foridentifying which lane the driver's vehicle is traveling in. The laneposition of the driver's vehicle may be identified by any other means.For example, by utilizing an ultra-wide band (UWB) technique, it ispossible to identify which one of a plurality of lanes the driver'svehicle is traveling in. It is widely known that the ultra-wide bandtechnique is applicable to position measurement and/or radar. Using theultra-wide band technique enhances the range resolution of the radar, sothat, even when a large number of vehicles exist ahead, each individualtarget can be detected with distinction, based on differences indistance. This makes it possible to identify distance from a guardrailon the road shoulder, or from the median strip. The width of each laneis predefined based on each country's law or the like. By using suchinformation, it becomes possible to identify where the lane in which thedriver's vehicle is currently traveling is. Note that the ultra-wideband technique is an example. A radio wave based on any other wirelesstechnique may be used. Moreover, LIDAR (Light Detection and Ranging) maybe used together with a radar. LIDAR is sometimes called “laser radar”.

The array antenna AA may be a generic millimeter wave array antenna foronboard use. The transmission antenna Tx in this Application Exampleradiates a millimeter wave as a transmission wave ahead of the vehicle.A portion of the transmission wave is reflected off a target which istypically a preceding vehicle, whereby a reflected wave occurs from thetarget being a wave source. A portion of the reflected wave reaches thearray antenna (reception antenna) AA as an arriving wave. Each of theplurality of antenna elements of the array antenna AA outputs areception signal in response to one or plural arriving waves. In thecase where the number of targets functioning as wave sources ofreflected waves is K (where K is an integer of one or more), the numberof arriving waves is K, but this number K of arriving waves is not knownbeforehand.

The example of FIG. 21 assumes that the radar system 510 is provided asan integral piece, including the array antenna AA, on the rearviewmirror. However, the number and positions of array antennas AA are notlimited to any specific number or specific positions. An array antennaAA may be disposed on the rear surface of the vehicle so as to be ableto detect targets that are behind the vehicle. Moreover, a plurality ofarray antennas AA may be disposed on the front surface and the rearsurface of the vehicle. The array antenna(s) AA may be disposed insidethe vehicle. Even in the case where a horn antenna whose respectiveantenna elements include horns as mentioned above is to be adopted asthe array antenna(s) AA, the array antenna(s) with such antenna elementsmay be situated inside the vehicle.

The signal processing circuit 560 receives and processes the receptionsignals which have been received by the reception antenna Rx andsubjected to preprocessing by the transmission/reception circuit 580.This process encompasses inputting the reception signals to the arrivingwave estimation unit AU, or alternatively, generating a secondarysignal(s) from the reception signals and inputting the secondarysignal(s) to the arriving wave estimation unit AU.

In the example of FIG. 23, a selection circuit 596 which receives thesignal being output from the signal processing circuit 560 and thesignal being output from the image processing circuit 720 is provided inthe object detection apparatus 570. The selection circuit 596 allows oneor both of the signal being output from the signal processing circuit560 and the signal being output from the image processing circuit 720 tobe fed to the travel assistance electronic control apparatus 520.

FIG. 24 is a block diagram showing a more detailed exemplaryconstruction of the radar system 510 according to this ApplicationExample.

As shown in FIG. 24, the array antenna AA includes a transmissionantenna Tx which transmits a millimeter wave and reception antennas Rxwhich receive arriving waves reflected from targets. Although only onetransmission antenna Tx is illustrated in the figure, two or more kindsof transmission antennas with different characteristics may be provided.The array antenna AA includes M antenna elements 11 ₁, 11 ₂, . . . , 11_(M) (where M is an integer of 3 or more). In response to the arrivingwaves, the plurality of antenna elements 11 ₁, 11 ₂, . . . , 11 _(M)respectively output reception signals s₁, s₂, . . . , s_(M) (FIG. 20B).

In the array antenna AA, the antenna elements 11 ₁ to 11 _(M) arearranged in a linear array or a two-dimensional array at fixedintervals, for example. Each arriving wave will impinge on the arrayantenna AA from a direction at an angle θ with respect to the normal ofthe plane in which the antenna elements 11 ₁ to 11 _(M) are arrayed.Thus, the direction of arrival of an arriving wave is defined by thisangle θ.

When an arriving wave from one target impinges on the array antenna AA,this approximates to a plane wave impinging on the antenna elements 11 ₁to 11 _(M) from azimuths of the same angle θ. When K arriving wavesimpinge on the array antenna AA from K targets with different azimuths,the individual arriving waves can be identified in terms of respectivelydifferent angles θ₁ to θ_(K).

As shown in FIG. 24, the object detection apparatus 570 includes thetransmission/reception circuit 580 and the signal processing circuit560.

The transmission/reception circuit 580 includes a triangular wavegeneration circuit 581, a VCO (voltage controlled oscillator) 582, adistributor 583, mixers 584, filters 585, a switch 586, an A/D converter587, and a controller 588. Although the radar system in this ApplicationExample is configured to perform transmission and reception ofmillimeter waves by the FMCW method, the radar system of the presentdisclosure is not limited to this method. The transmission/receptioncircuit 580 is configured to generate a beat signal based on a receptionsignal from the array antenna AA and a transmission signal from thetransmission antenna Tx.

The signal processing circuit 560 includes a distance detection section533, a velocity detection section 534, and an azimuth detection section536. The signal processing circuit 560 is configured to process a signalfrom the A/D converter 587 in the transmission/reception circuit 580,and output signals respectively indicating the detected distance to thetarget, the relative velocity of the target, and the azimuth of thetarget.

First, the construction and operation of the transmission/receptioncircuit 580 will be described in detail.

The triangular wave generation circuit 581 generates a triangular wavesignal, and supplies it to the VCO 582. The VCO 582 outputs atransmission signal having a frequency as modulated based on thetriangular wave signal. FIG. 25 is a diagram showing change in frequencyof a transmission signal which is modulated based on the signal that isgenerated by the triangular wave generation circuit 581. This waveformhas a modulation width Δf and a center frequency of f0. The transmissionsignal having a thus modulated frequency is supplied to the distributor583. The distributor 583 allows the transmission signal obtained fromthe VCO 582 to be distributed among the mixers 584 and the transmissionantenna Tx. Thus, the transmission antenna radiates a millimeter wavehaving a frequency which is modulated in triangular waves, as shown inFIG. 25.

In addition to the transmission signal, FIG. 25 also shows an example ofa reception signal from an arriving wave which is reflected from asingle preceding vehicle. The reception signal is delayed from thetransmission signal. This delay is in proportion to the distance betweenthe driver's vehicle and the preceding vehicle. Moreover, the frequencyof the reception signal increases or decreases in accordance with therelative velocity of the preceding vehicle, due to the Doppler effect.

When the reception signal and the transmission signal are mixed, a beatsignal is generated based on their frequency difference. The frequencyof this beat signal (beat frequency) differs between a period in whichthe transmission signal increases in frequency (ascent) and a period inwhich the transmission signal decreases in frequency (descent). Once abeat frequency for each period is determined, based on such beatfrequencies, the distance to the target and the relative velocity of thetarget are calculated.

FIG. 26 shows a beat frequency fu in an “ascent” period and a beatfrequency fd in a “descent” period. In the graph of FIG. 26, thehorizontal axis represents frequency, and the vertical axis representssignal intensity. This graph is obtained by subjecting the beat signalto time-frequency conversion. Once the beat frequencies fu and fd areobtained, based on a known equation, the distance to the target and therelative velocity of the target are calculated. In this ApplicationExample, with the construction and operation described below, beatfrequencies corresponding to each antenna element of the array antennaAA are obtained, thus enabling estimation of the position information ofa target.

In the example shown in FIG. 24, reception signals from channels Ch₁ toCh_(M) corresponding to the respective antenna elements 11 ₁ to 11 _(M)are each amplified by an amplifier, and input to the correspondingmixers 584. Each mixer 584 mixes the transmission signal into theamplified reception signal. Through this mixing, a beat signal isgenerated corresponding to the frequency difference between thereception signal and the transmission signal. The generated beat signalis fed to the corresponding filter 585. The filters 585 apply bandwidthcontrol to the beat signals on the channels Ch₁ to Ch_(M), and supplybandwidth-controlled beat signals to the switch 586.

The switch 586 performs switching in response to a sampling signal whichis input from the controller 588. The controller 588 may be composed ofa microcomputer, for example. Based on a computer program which isstored in a memory such as a ROM, the controller 588 controls the entiretransmission/reception circuit 580. The controller 588 does not need tobe provided inside the transmission/reception circuit 580, but may beprovided inside the signal processing circuit 560. In other words, thetransmission/reception circuit 580 may operate in accordance with acontrol signal from the signal processing circuit 560. Alternatively,some or all of the functions of the controller 588 may be realized by acentral processing unit which controls the entire transmission/receptioncircuit 580 and signal processing circuit 560.

The beat signals on the channels Ch₁ to Ch_(M) having passed through therespective filters 585 are consecutively supplied to the A/D converter587 via the switch 586. In synchronization with the sampling signal, theA/D converter 587 converts the beat signals on the channels Ch₁ toCh_(M), which are input from the switch 586, into digital signals.

Hereinafter, the construction and operation of the signal processingcircuit 560 will be described in detail. In this Application Example,the distance to the target and the relative velocity of the target areestimated by the FMCW method. Without being limited to the FMCW methodas described below, the radar system can also be implemented by usingother methods, e.g., 2 frequency CW and spread spectrum methods.

In the example shown in FIG. 24, the signal processing circuit 560includes a memory 531, a reception intensity calculation section 532, adistance detection section 533, a velocity detection section 534, a DBF(digital beam forming) processing section 535, an azimuth detectionsection 536, a target link processing section 537, a matrix generationsection 538, a target output processing section 539, and an arrivingwave estimation unit AU. As mentioned earlier, a part or a whole of thesignal processing circuit 560 may be implemented by FPGA, or by a set ofa general-purpose processor(s) and a main memory device(s). The memory531, the reception intensity calculation section 532, the DBF processingsection 535, the distance detection section 533, the velocity detectionsection 534, the azimuth detection section 536, the target linkprocessing section 537, and the arriving wave estimation unit AU may beindividual parts that are implemented in distinct pieces of hardware, orfunctional blocks of a single signal processing circuit.

FIG. 27 shows an exemplary implementation in which the signal processingcircuit 560 is implemented in hardware including a processor PR and amemory device MD. In the signal processing circuit 560 with thisconstruction, too, a computer program that is stored in the memorydevice MD may fulfill the functions of the reception intensitycalculation section 532, the DBF processing section 535, the distancedetection section 533, the velocity detection section 534, the azimuthdetection section 536, the target link processing section 537, thematrix generation section 538, and the arriving wave estimation unit AUshown in FIG. 24.

The signal processing circuit 560 in this Application Example isconfigured to estimate the position information of a preceding vehicleby using each beat signal converted into a digital signal as a secondarysignal of the reception signal, and output a signal indicating theestimation result. Hereinafter, the construction and operation of thesignal processing circuit 560 in this Application Example will bedescribed in detail.

For each of the channels Ch₁ to Ch_(M), the memory 531 in the signalprocessing circuit 560 stores a digital signal which is output from theA/D converter 587. The memory 531 may be composed of a generic storagemedium such as a semiconductor memory or a hard disk and/or an opticaldisk.

The reception intensity calculation section 532 applies Fouriertransform to the respective beat signals for the channels Ch₁ to Ch_(M)(shown in the lower graph of FIG. 25) that are stored in the memory 531.In the present specification, the amplitude of a piece of complex numberdata after the Fourier transform is referred to as “signal intensity”.The reception intensity calculation section 532 converts the complexnumber data of a reception signal from one of the plurality of antennaelements, or a sum of the complex number data of all reception signalsfrom the plurality of antenna elements, into a frequency spectrum. Inthe resultant spectrum, beat frequencies corresponding to respectivepeak values, which are indicative of presence and distance of targets(preceding vehicles), can be detected. Taking a sum of the complexnumber data of the reception signals from all antenna elements willallow the noise components to average out, whereby the S/N ratio isimproved.

In the case where there is one target, i.e., one preceding vehicle, asshown in FIG. 26, the Fourier transform will produce a spectrum havingone peak value in a period of increasing frequency (the “ascent” period)and one peak value in a period of decreasing frequency (“the descent”period). The beat frequency of the peak value in the “ascent” period isdenoted by “fu”, whereas the beat frequency of the peak value in the“descent” period is denoted by “fd”.

From the signal intensities of beat frequencies, the reception intensitycalculation section 532 detects any signal intensity that exceeds apredefined value (threshold value), thus determining the presence of atarget. Upon detecting a signal intensity peak, the reception intensitycalculation section 532 outputs the beat frequencies (fu, fd) of thepeak values to the distance detection section 533 and the velocitydetection section 534 as the frequencies of the object of interest. Thereception intensity calculation section 532 outputs informationindicating the frequency modulation width Δf to the distance detectionsection 533, and outputs information indicating the center frequency f0to the velocity detection section 534.

In the case where signal intensity peaks corresponding to plural targetsare detected, the reception intensity calculation section 532 findassociations between the ascents peak values and the descent peak valuesbased on predefined conditions. Peaks which are determined as belongingto signals from the same target are given the same number, and thus arefed to the distance detection section 533 and the velocity detectionsection 534.

When there are plural targets, after the Fourier transform, as manypeaks as there are targets will appear in the ascent portions and thedescent portions of the beat signal. In proportion to the distancebetween the radar and a target, the reception signal will become moredelayed and the reception signal in FIG. 25 will shift more toward theright. Therefore, a beat signal will have a greater frequency as thedistant between the target and the radar increases.

Based on the beat frequencies fu and fd which are input from thereception intensity calculation section 532, the distance detectionsection 533 calculates a distance R through the equation below, andsupplies it to the target link processing section 537.R={c·T/(2·Δf)}·{(fu+fd)/2}

Moreover, based on the beat frequencies fu and fd being input from thereception intensity calculation section 532, the velocity detectionsection 534 calculates a relative velocity V through the equation below,and supplies it to the target link processing section 537.V={c/(2·f0)}·{(fu−fd)/2}

In the equation which calculates the distance R and the relativevelocity V, c is velocity of light, and T is the modulation period.

Note that the lower limit resolution of distance R is expressed asc/(2Δf). Therefore, as Δf increases, the resolution of distance Rincreases. In the case where the frequency f0 is in the 76 GHz band,when Δf is set on the order of 660 megahertz (MHz), the resolution ofdistance R will be on the order of 0.23 meters (m), for example.Therefore, if two preceding vehicles are traveling abreast of eachother, it may be difficult with the FMCW method to identify whetherthere is one vehicle or two vehicles. In such a case, it might bepossible to run an algorithm for direction-of-arrival estimation thathas an extremely high angular resolution to separate between theazimuths of the two preceding vehicles and enable detection.

By utilizing phase differences between signals from the antenna elements11 ₂, 11 ₂, . . . , 11 _(M), the DBF processing section 535 allows theincoming complex data corresponding to the respective antenna elements,which has been Fourier transformed with respect to the time axis, to beFourier transformed with respect to the direction in which the antennaelements are arrayed. Then, the DBF processing section 535 calculatesspatial complex number data indicating the spectrum intensity for eachangular channel as determined by the angular resolution, and outputs itto the azimuth detection section 536 for the respective beatfrequencies.

The azimuth detection section 536 is provided for the purpose ofestimating the azimuth of a preceding vehicle. Among the values ofspatial complex number data that has been calculated for the respectivebeat frequencies, the azimuth detection section 536 chooses an angle θthat takes the largest value, and outputs it to the target linkprocessing section 537 as the azimuth at which an object of interestexists.

Note that the method of estimating the angle θ indicating the directionof arrival of an arriving wave is not limited to this example. Variousalgorithms for direction-of-arrival estimation that have been mentionedearlier can be employed.

The target link processing section 537 calculates absolute values of thedifferences between the respective values of distance, relativevelocity, and azimuth of the object of interest as calculated in thecurrent cycle and the respective values of distance, relative velocity,and azimuth of the object of interest as calculated 1 cycle before,which are read from the memory 531. Then, if the absolute value of eachdifference is smaller than a value which is defined for the respectivevalue, the target link processing section 537 determines that the targetthat was detected 1 cycle before and the target detected in the currentcycle are an identical target. In that case, the target link processingsection 537 increments the count of target link processes, which is readfrom the memory 531, by one.

If the absolute value of a difference is greater than predetermined, thetarget link processing section 537 determines that a new object ofinterest has been detected. The target link processing section 537stores the respective values of distance, relative velocity, and azimuthof the object of interest as calculated in the current cycle and alsothe count of target link processes for that object of interest to thememory 531.

In the signal processing circuit 560, the distance to the object ofinterest and its relative velocity can be detected by using a spectrumwhich is obtained through a frequency analysis of beat signals, whichare signals generated based on received reflected waves.

The matrix generation section 538 generates a spatial covariance matrixby using the respective beat signals for the channels Ch₁ to Ch_(M)(lower graph in FIG. 25) stored in the memory 531. In the spatialcovariance matrix of Math. 4, each component is the value of a beatsignal which is expressed in terms of real and imaginary parts. Thematrix generation section 538 further determines eigenvalues of thespatial covariance matrix Rxx, and inputs the resultant eigenvalueinformation to the arriving wave estimation unit AU.

When a plurality of signal intensity peaks corresponding to pluralobjects of interest have been detected, the reception intensitycalculation section 532 numbers the peak values respectively in theascent portion and in the descent portion, beginning from those withsmaller frequencies first, and output them to the target outputprocessing section 539. In the ascent and descent portions, peaks of anyidentical number correspond to the same object of interest. Theidentification numbers are to be regarded as the numbers assigned to theobjects of interest. For simplicity of illustration, a leader line fromthe reception intensity calculation section 532 to the target outputprocessing section 539 is conveniently omitted from FIG. 24.

When the object of interest is a structure ahead, the target outputprocessing section 539 outputs the identification number of that objectof interest as indicating a target. When receiving results ofdetermination concerning plural objects of interest, such that all ofthem are structures ahead, the target output processing section 539outputs the identification number of an object of interest that is inthe lane of the driver's vehicle as the object position informationindicating where a target is. Moreover, When receiving results ofdetermination concerning plural objects of interest, such that all ofthem are structures ahead and that two or more objects of interest arein the lane of the driver's vehicle, the target output processingsection 539 outputs the identification number of an object of interestthat is associated with the largest count of target being read from thelink processes memory 531 as the object position information indicatingwhere a target is.

Referring back to FIG. 23, an example where the onboard radar system 510is incorporated in the exemplary construction shown in FIG. 23 will bedescribed. The image processing circuit 720 acquires information of anobject from the video, and detects target position information from theobject information. For example, the image processing circuit 720 isconfigured to estimate distance information of an object by detectingthe depth value of an object within an acquired video, or detect sizeinformation and the like of an object from characteristic amounts in thevideo, thus detecting position information of the object.

The selection circuit 596 selectively feeds position information whichis received from the signal processing circuit 560 or the imageprocessing circuit 720 to the travel assistance electronic controlapparatus 520. For example, the selection circuit 596 compares a firstdistance, i.e., the distance from the driver's vehicle to a detectedobject as contained in the object position information from the signalprocessing circuit 560, against a second distance, i.e., the distancefrom the driver's vehicle to the detected object as contained in theobject position information from the image processing circuit 720, anddetermines which is closer to the driver's vehicle. For example, basedon the result of determination, the selection circuit 596 may select theobject position information which indicates a closer distance to thedriver's vehicle, and output it to the travel assistance electroniccontrol apparatus 520. If the result of determination indicates thefirst distance and the second distance to be of the same value, theselection circuit 596 may output either one, or both of them, to thetravel assistance electronic control apparatus 520.

If information indicating that there is no prospective target is inputfrom the reception intensity calculation section 532, the target outputprocessing section 539 (FIG. 24) outputs zero, indicating that there isno target, as the object position information. Then, on the basis of theobject position information from the target output processing section539, through comparison against a predefined threshold value, theselection circuit 596 chooses either the object position informationfrom the signal processing circuit 560 or the object positioninformation from the image processing circuit 720 to be used.

Based on predefined conditions, the travel assistance electronic controlapparatus 520 having received the position information of a precedingobject from the object detection apparatus 570 performs control to makethe operation safer or easier for the driver who is driving the driver'svehicle, in accordance with the distance and size indicated by theobject position information, the velocity of the driver's vehicle, roadsurface conditions such as rainfall, snowfall or clear weather, or otherconditions. For example, if the object position information indicatesthat no object has been detected, the travel assistance electroniccontrol apparatus 520 may send a control signal to an acceleratorcontrol circuit 526 to increase speed up to a predefined velocity,thereby controlling the accelerator control circuit 526 to make anoperation that is equivalent to stepping on the accelerator pedal.

In the case where the object position information indicates that anobject has been detected, if it is found to be at a predetermineddistance from the driver's vehicle, the travel assistance electroniccontrol apparatus 520 controls the brakes via a brake control circuit524 through a brake-by-wire construction or the like. In other words, itmakes an operation of decreasing the velocity to maintain a constantvehicular gap. Upon receiving the object position information, thetravel assistance electronic control apparatus 520 sends a controlsignal to an alarm control circuit 522 so as to control lampillumination or control audio through a loudspeaker which is providedwithin the vehicle, so that the driver is informed of the nearing of apreceding object. Upon receiving object position information including aspatial distribution of preceding vehicles, the travel assistanceelectronic control apparatus 520 may, if the traveling velocity iswithin a predefined range, automatically make the steering wheel easierto operate to the right or left, or control the hydraulic pressure onthe steering wheel side so as to force a change in the direction of thewheels, thereby providing assistance in collision avoidance with respectto the preceding object.

The object detection apparatus 570 may be arranged so that, if a pieceof object position information which was being continuously detected bythe selection circuit 596 for a while in the previous detection cyclebut which is not detected in the current detection cycle becomesassociated with a piece of object position information from acamera-detected video indicating a preceding object, then continuedtracking is chosen, and object position information from the signalprocessing circuit 560 is output with priority.

An exemplary specific construction and an exemplary operation for theselection circuit 596 to make a selection between the outputs from thesignal processing circuit 560 and the image processing circuit 720 aredisclosed in the specification of U.S. Pat. No. 8,446,312, thespecification of U.S. Pat. No. 8,730,096, and the specification of U.S.Pat. No. 8,730,099. The entire disclosure thereof is incorporated hereinby reference.

[First Variant]

In the radar system for onboard use of the above Application Example,the (sweep) condition for a single instance of FMCW (Frequency ModulatedContinuous Wave) frequency modulation, i.e., a time span required forsuch a modulation (sweep time), is e.g. 1 millisecond, although thesweep time could be shortened to about 100 microseconds.

However, in order to realize such a rapid sweep condition, not only theconstituent elements involved in the radiation of a transmission wave,but also the constituent elements involved in the reception under thatsweep condition must also be able to rapidly operate. For example, anA/D converter 587 (FIG. 24) which rapidly operates under that sweepcondition will be needed. The sampling frequency of the A/D converter587 may be 10 MHz, for example. The sampling frequency may be fasterthan 10 MHz.

In the present variant, a relative velocity with respect to a target iscalculated without utilizing any Doppler shift-based frequencycomponent. In this variant, the sweep time is Tm=100 microseconds, whichis very short. The lowest frequency of a detectable beat signal, whichis 1/Tm, equals 10 kHz in this case. This would correspond to a Dopplershift of a reflected wave from a target which has a relative velocity ofapproximately 20 m/second. In other words, so long as one relies on aDoppler shift, it would be impossible to detect relative velocities thatare equal to or smaller than this. Thus, a method of calculation whichis different from a Doppler shift-based method of calculation ispreferably adopted.

As an example, this variant illustrates a process that utilizes a signal(upbeat signal) representing a difference between a transmission waveand a reception wave which is obtained in an upbeat (ascent) portionwhere the transmission wave increases in frequency. A single sweep timeof FMCW is 100 microseconds, and its waveform is a sawtooth shape whichis composed only of an upbeat portion. In other words, in this variant,the signal wave which is generated by the triangular wave/CW wavegeneration circuit 581 has a sawtooth shape. The sweep width infrequency is 500 MHz. Since no peaks are to be utilized that areassociated with Doppler shifts, the process is not one that generates anupbeat signal and a downbeat signal to utilize the peaks of both, butwill rely on only one of such signals. Although a case of utilizing anupbeat signal will be illustrated herein, a similar process can also beperformed by using a downbeat signal.

The A/D converter 587 (FIG. 24) samples each upbeat signal at a samplingfrequency of 10 MHz, and outputs several hundred pieces of digital data(hereinafter referred to as “sampling data”). The sampling data isgenerated based on upbeat signals after a point in time where areception wave is obtained and until a point in time at which atransmission wave completes transmission, for example. Note that theprocess may be ended as soon as a certain number of pieces of samplingdata are obtained.

In this variant, 128 upbeat signals are transmitted/received in series,for each of which some several hundred pieces of sampling data areobtained. The number of upbeat signals is not limited to 128. It may be256, or 8. An arbitrary number may be selected depending on the purpose.

The resultant sampling data is stored to the memory 531. The receptionintensity calculation section 532 applies a two-dimensional fast Fouriertransform (FFT) to the sampling data. Specifically, first, for each ofthe sampling data pieces that have been obtained through a single sweep,a first FFT process (frequency analysis process) is performed togenerate a power spectrum. Next, the velocity detection section 534performs a second FFT process for the processing results that have beencollected from all sweeps.

When the reflected waves are from the same target, peak components inthe power spectrum to be detected in each sweep period will be of thesame frequency. On the other hand, for different targets, the peakcomponents will differ in frequency. Through the first FFT process,plural targets that are located at different distances can be separated.

In the case where a relative velocity with respect to a target isnon-zero, the phase of the upbeat signal changes slightly from sweep tosweep. In other words, through the second FFT process, a power spectrumwhose elements are the data of frequency components that are associatedwith such phase changes will be obtained for the respective results ofthe first FFT process.

The reception intensity calculation section 532 extracts peak values inthe second power spectrum above, and sends them to the velocitydetection section 534.

The velocity detection section 534 determines a relative velocity fromthe phase changes. For example, suppose that a series of obtained upbeatsignals undergo phase changes by every phase θ [RXd]. Assuming that thetransmission wave has an average wavelength λ, this means there is aλ/(4π/θ) change in distance every time an upbeat signal is obtained.Since this change has occurred over an interval of upbeat signaltransmission Tm (=100 microseconds), the relative velocity is determinedto be {λ/(4π/θ)}/Tm.

Through the above processes, a relative velocity with respect to atarget as well as a distance from the target can be obtained.

[Second Variant]

The radar system 510 is able to detect a target by using a continuouswave(s) CW of one or plural frequencies. This method is especiallyuseful in an environment where a multitude of reflected waves impinge onthe radar system 510 from still objects in the surroundings, e.g., whenthe vehicle is in a tunnel.

The radar system 510 has an antenna array for reception purposes,including five channels of independent reception elements. In such aradar system, the azimuth-of-arrival estimation for incident reflectedwaves is only possible if there are four or fewer reflected waves thatare simultaneously incident. In an FMCW-type radar, the number ofreflected waves to be simultaneously subjected to an azimuth-of-arrivalestimation can be reduced by exclusively selecting reflected waves froma specific distance. However, in an environment where a large number ofstill objects exist in the surroundings, e.g., in a tunnel, it is as ifthere were a continuum of objects to reflect radio waves; therefore,even if one narrows down on the reflected waves based on distance, thenumber of reflected waves may still not be equal to or smaller thanfour. However, any such still object in the surroundings will have anidentical relative velocity with respect to the driver's vehicle, andthe relative velocity will be greater than that associated with anyother vehicle that is traveling ahead. On this basis, such still objectscan be distinguished from any other vehicle based on the magnitudes ofDoppler shifts.

Therefore, the radar system 510 performs a process of: radiatingcontinuous waves CW of plural frequencies; and, while ignoring Dopplershift peaks that correspond to still objects in the reception signals,detecting a distance by using a Doppler shift peak(s) of any smallershift amount(s). Unlike in the FMCW method, in the CW method, afrequency difference between a transmission wave and a reception wave isascribable only to a Doppler shift. In other words, any peak frequencythat appears in a beat signal is ascribable only to a Doppler shift.

In the description of this variant, too, a continuous wave to be used inthe CW method will be referred to as a “continuous wave CW”. Asdescribed above, a continuous wave CW has a constant frequency; that is,it is unmodulated.

Suppose that the radar system 510 has radiated a continuous wave CW of afrequency fp, and detected a reflected wave of a frequency fq that hasbeen reflected off a target. The difference between the transmissionfrequency fp and the reception frequency fq is called a Dopplerfrequency, which approximates to fp−fq=2·Vr·fp/c. Herein, Vr is arelative velocity between the radar system and the target, and c is thevelocity of light. The transmission frequency fp, the Doppler frequency(fp-fq), and the velocity of light c are known. Therefore, from thisequation, the relative velocity Vr=(fp−fq)·c/2fp can be determined. Thedistance to the target is calculated by utilizing phase information aswill be described later.

In order to detect a distance to a target by using continuous waves CW,a 2 frequency CW method is adopted. In the 2 frequency CW method,continuous waves CW of two frequencies which are slightly apart areradiated each for a certain period, and their respective reflected wavesare acquired. For example, in the case of using frequencies in the 76GHz band, the difference between the two frequencies would be severalhundred kHz. As will be described later, it is more preferable todetermine the difference between the two frequencies while taking intoaccount the minimum distance at which the radar used is able to detect atarget.

Suppose that the radar system 510 has sequentially radiated continuouswaves CW of frequencies fp1 and fp2 (fp1<fp2), and that the twocontinuous waves CW have been reflected off a single target, resultingin reflected waves of frequencies fq1 and fq2 being received by theradar system 510.

Based on the continuous wave CW of the frequency fp1 and the reflectedwave (frequency fq1) thereof, a first Doppler frequency is obtained.Based on the continuous wave CW of the frequency fp2 and the reflectedwave (frequency fq2) thereof, a second Doppler frequency is obtained.The two Doppler frequencies have substantially the same value. However,due to the difference between the frequencies fp1 and fp2, the complexsignals of the respective reception waves differ in phase. By utilizingthis phase information, a distance (range) to the target can becalculated.

Specifically, the radar system 510 is able to determine the distance Ras R=c·Δφ/4π(fp2−fp1). Herein, Δφ denotes the phase difference betweentwo beat signals, i.e., beat signal 1 which is obtained as a differencebetween the continuous wave CW of the frequency fp1 and the reflectedwave (frequency fq1) thereof and beat signal 2 which is obtained as adifference between the continuous wave CW of the frequency fp2 and thereflected wave (frequency fq2) thereof. The method of identifying thefrequency fb1 of beat signal 1 and the frequency fb2 of beat signal 2 isidentical to that in the aforementioned instance of a beat signal from acontinuous wave CW of a single frequency.

Note that a relative velocity Vr under the 2 frequency CW method isdetermined as follows.Vr=fb1·c/2·fp1 or Vr=fb2·c/2·fp2

Moreover, the range in which a distance to a target can be uniquelyidentified is limited to the range defined by Rmax<c/2(fp2−fp1). Thereason is that beat signals resulting from a reflected wave from anyfarther target would produce a Δφ which is greater than 2π, such thatthey are indistinguishable from beat signals associated with targets atcloser positions. Therefore, it is more preferable to adjust thedifference between the frequencies of the two continuous waves CW sothat Rmax becomes greater than the minimum detectable distance of theradar. In the case of a radar whose minimum detectable distance is 100m, fp2−fp1 may be made e.g. 1.0 MHz. In this case, Rmax=150 m, so that asignal from any target from a position beyond Rmax is not detected. Inthe case of mounting a radar which is capable of detection up to 250 m,fp2−fp1 may be made e.g. 500 kHz. In this case, Rmax=300 m, so that asignal from any target from a position beyond Rmax is not detected,either. In the case where the radar has both of an operation mode inwhich the minimum detectable distance is 100 m and the horizontalviewing angle is 120 degrees and an operation mode in which the minimumdetectable distance is 250 m and the horizontal viewing angle is 5degrees, it is preferable to switch the fp2−fp1 value be 1.0 MHz and 500kHz for operation in the respective operation modes.

A detection approach is known which, by transmitting continuous waves CWat N different frequencies (where N is an integer of 3 or more), andutilizing phase information of the respective reflected waves, detects adistance to each target. Under this detection approach, distance can beproperly recognized up to N−1 targets. As the processing to enable this,a fast Fourier transform (FFT) is used, for example. Given N=64 or 128,an FFT is performed for sampling data of a beat signal as a differencebetween a transmission signal and a reception signal for each frequency,thus obtaining a frequency spectrum (relative velocity). Thereafter, atthe frequency of the CW wave, a further FFT is performed for peaks ofthe same frequency, thus to derive distance information.

Hereinafter, this will be described more specifically.

For ease of explanation, first, an instance will be described wheresignals of three frequencies f1, f2 and f3 are transmitted while beingswitched over time. It is assumed that f1>f2>f3, and f1−f2=f2−f3=Δf. Atransmission time Δt is assumed for the signal wave for each frequency.FIG. 28 shows a relationship between three frequencies f1, f2 and f3.

Via the transmission antenna Tx, the triangular wave/CW wave generationcircuit 581 (FIG. 24) transmits continuous waves CW of frequencies f1,f2 and f3, each lasting for the time Δt. The reception antennas Rxreceive reflected waves resulting by the respective continuous waves CWbeing reflected off one or plural targets.

Each mixer 584 mixes a transmission wave and a reception wave togenerate a beat signal. The A/D converter 587 converts the beat signal,which is an analog signal, into several hundred pieces of digital data(sampling data), for example.

Using the sampling data, the reception intensity calculation section 532performs FFT computation. Through the FFT computation, frequencyspectrum information of reception signals is obtained for the respectivetransmission frequencies f1, f2 and f3.

Thereafter, the reception intensity calculation section 532 separatespeak values from the frequency spectrum information of the receptionsignals. The frequency of any peak value which is predetermined orgreater is in proportion to a relative velocity with respect to atarget. Separating a peak value(s) from the frequency spectruminformation of reception signals is synonymous with separating one orplural targets with different relative velocities.

Next, with respect to each of the transmission frequencies f1 to f3, thereception intensity calculation section 532 measures spectruminformation of peak values of the same relative velocity or relativevelocities within a predefined range.

Now, consider a scenario where two targets A and B exist which haveabout the same relative velocity but are at respectively differentdistances. A transmission signal of the frequency f1 will be reflectedfrom both of targets A and B to result in reception signals beingobtained. The reflected waves from targets A and B will result insubstantially the same beat signal frequency. Therefore, the powerspectra at the Doppler frequencies of the reception signals,corresponding to their relative velocities, are obtained as a syntheticspectrum F1 into which the power spectra of two targets A and B havebeen merged.

Similarly, for each of the frequencies f2 and f3, the power spectra atthe Doppler frequencies of the reception signals, corresponding to theirrelative velocities, are obtained as a synthetic spectrum F1 into whichthe power spectra of two targets A and B have been merged.

FIG. 29 shows a relationship between synthetic spectra F1 to F3 on acomplex plane. In the directions of the two vectors composing each ofthe synthetic spectra F1 to F3, the right vector corresponds to thepower spectrum of a reflected wave from target A; i.e., vectors f1A, f2Aand f3A, in FIG. 29. On the other hand, in the directions of the twovectors composing each of the synthetic spectra F1 to F3, the leftvector corresponds to the power spectrum of a reflected wave from targetB; i.e., vectors f1B, f2B and f3B in FIG. 29.

Under a constant difference Δf between the transmission frequencies, thephase difference between the reception signals corresponding to therespective transmission signals of the frequencies f1 and f2 is inproportion to the distance to a target. Therefore, the phase differencebetween the vectors f1A and f2A and the phase difference between thevectors f2A and f3A are of the same value θA, this phase difference OAbeing in proportion to the distance to target A. Similarly, the phasedifference between the vectors f1B and f2B and the phase differencebetween the vectors f2B and f3B are of the same value θB, this phasedifference θB being in proportion to the distance to target B.

By using a well-known method, the respective distances to targets A andB can be determined from the synthetic spectra F1 to F3 and thedifference Δf between the transmission frequencies. This technique isdisclosed in U.S. Pat. No. 6,703,967, for example. The entire disclosureof this publication is incorporated herein by reference.

Similar processing is also applicable when the transmitted signals havefour or more frequencies.

Note that, before transmitting continuous wave CWs at N differentfrequencies, a process of determining the distance to and relativevelocity of each target may be performed by the 2 frequency CW method.Then, under predetermined conditions, this process may be switched to aprocess of transmitting continuous waves CW at N different frequencies.For example, FFT computation may be performed by using the respectivebeat signals at the two frequencies, and if the power spectrum of eachtransmission frequency undergoes a change over time of 30% or more, theprocess may be switched. The amplitude of a reflected wave from eachtarget undergoes a large change over time due to multipath influencesand the like. When there exists a change of a predetermined magnitude orgreater, it may be considered that plural targets may exist.

Moreover, the CW method is known to be unable to detect a target whenthe relative velocity between the radar system and the target is zero,i.e., when the Doppler frequency is zero. However, when a pseudo Dopplersignal is determined by the following methods, for example, it ispossible to detect a target by using that frequency.

(Method 1) A mixer that causes a certain frequency shift in the outputof a receiving antenna is added. By using a transmission signal and areception signal with a shifted frequency, a pseudo Doppler signal canbe obtained.

(Method 2) A variable phase shifter to introduce phase changescontinuously over time is inserted between the output of a receivingantenna and a mixer, thus adding a pseudo phase difference to thereception signal. By using a transmission signal and a reception signalwith an added phase difference, a pseudo Doppler signal can be obtained.

An example of specific construction and operation of inserting avariable phase shifter to generate a pseudo Doppler signal under Method2 is disclosed in Japanese Laid-Open Patent Publication No. 2004-257848.The entire disclosure of this publication is incorporated herein byreference.

When targets with zero or very little relative velocity need to bedetected, the aforementioned processes of generating a pseudo Dopplersignal may be adopted, or the process may be switched to a targetdetection process under the FMCW method.

Next, with reference to FIG. 30, a procedure of processing to beperformed by the object detection apparatus 570 of the onboard radarsystem 510 will be described.

The example below will illustrate a case where continuous waves CW aretransmitted at two different frequencies fp1 and fp2 (fp1<fp2), and thephase information of each reflected wave is utilized to respectivelydetect a distance with respect to a target.

FIG. 30 is a flowchart showing the procedure of a process of determiningrelative velocity and distance according to this variant.

At step S41, the triangular wave/CW wave generation circuit 581generates two continuous waves CW of frequencies which are slightlyapart, i.e., frequencies fp1 and fp2.

At step S42, the transmission antenna Tx and the reception antennas Rxperform transmission/reception of the generated series of continuouswaves CW. Note that the process of step S41 and the process of step S42are to be performed in parallel fashion respectively by the triangularwave/CW wave generation circuit 581 and the transmission antenna elementTx/reception antenna Rx, rather than step S42 following only aftercompletion of step S41.

At step S43, each mixer 584 generates a difference signal by utilizingeach transmission wave and each reception wave, whereby two differencesignals are obtained. Each reception wave is inclusive of a receptionwave emanating from a still object and a reception wave emanating from atarget. Therefore, next, a process of identifying frequencies to beutilized as the beat signals is performed. Note that the process of stepS41, the process of step S42, and the process of step S43 are to beperformed in parallel fashion by the triangular wave/CW wave generationcircuit 581, the transmission antenna Tx/reception antenna Rx, and themixers 584, rather than step S42 following only after completion of stepS41, or step S43 following only after completion of step S42.

At step S44, for each of the two difference signals, the objectdetection apparatus 570 identifies certain peak frequencies to befrequencies fb1 and fb2 of beat signals, such that these frequencies areequal to or smaller than a frequency which is predefined as a thresholdvalue and yet they have amplitude values which are equal to or greaterthan a predetermined amplitude value, and that the difference betweenthe two frequencies is equal to or smaller than a predetermined value.

At step S45, based on one of the two beat signal frequencies identified,the reception intensity calculation section 532 detects a relativevelocity. The reception intensity calculation section 532 calculates therelative velocity according to Vr=fb1·c/2·fp1, for example. Note that arelative velocity may be calculated by utilizing each of the two beatsignal frequencies, which will allow the reception intensity calculationsection 532 to verify whether they match or not, thus enhancing theprecision of relative velocity calculation.

At step S46, the reception intensity calculation section 532 determinesa phase difference Δφ between two beat signals 1 and 2, and determines adistance R=c·Δφ/4π(fp2−fp1) to the target.

Through the above processes, the relative velocity and distance to atarget can be detected.

Note that continuous waves CW may be transmitted at N differentfrequencies (where N is 3 or more), and by utilizing phase informationof the respective reflected wave, distances to plural targets which areof the same relative velocity but at different positions may bedetected.

In addition to the radar system 510, the vehicle 500 described above mayfurther include another radar system. For example, the vehicle 500 mayfurther include a radar system having a detection range toward the rearor the sides of the vehicle body. In the case of incorporating a radarsystem having a detection range toward the rear of the vehicle body, theradar system may monitor the rear, and if there is any danger of havinganother vehicle bump into the rear, make a response by issuing an alarm,for example. In the case of incorporating a radar system having adetection range toward the sides of the vehicle body, the radar systemmay monitor an adjacent lane when the driver's vehicle changes its lane,etc., and make a response by issuing an alarm or the like as necessary.

The applications of the above-described radar system 510 are not limitedto onboard use only. Rather, the radar system 510 may be used as sensorsfor various purposes. For example, it may be used as a radar formonitoring the surroundings of a house or any other building.

Alternatively, it may be used as a sensor for detecting the presence orabsence of a person at a specific indoor place, or whether or not such aperson is undergoing any motion, etc., without utilizing any opticalimages.

[Supplementary Details of Processing]

Other embodiments will be described in connection with the 2 frequencyCW or FMCW techniques for array antennas as described above. Asdescribed earlier, in the example of FIG. 24, the reception intensitycalculation section 532 applies a Fourier transform to the respectivebeat signals for the channels Ch₁ to Ch_(M) (lower graph in FIG. 25)stored in the memory 531. These beat signals are complex signals, inorder that the phase of the signal of computational interest beidentified. This allows the direction of an arriving wave to beaccurately identified. In this case, however, the computational load forFourier transform increases, thus calling for a larger-scaled circuit.

In order to solve this problem, a scalar signal may be generated as abeat signal. For each of a plurality of beat signals that have beengenerated, two complex Fourier transforms may be performed with respectto the spatial axis direction, which conforms to the antenna array, andto the time axis direction, which conforms to the lapse of time, thus toobtain results of frequency analysis. As a result, with only a smallamount of computation, beam formation can eventually be achieved so thatdirections of arrival of reflected waves can be identified, wherebyresults of frequency analysis can be obtained for the respective beams.As a patent document related to the present disclosure, the entiredisclosure of the specification of U.S. Pat. No. 6,339,395 isincorporated herein by reference.

[Optical Sensor, e.g., Camera, and Millimeter Wave Radar]

Next, a comparison between the above-described array antenna andconventional antennas, as well as an exemplary application in which bothof the present array antenna and an optical sensor (e.g., a camera) areutilized, will be described. Note that LIDAR or the like may be employedas the optical sensor.

A millimeter wave radar is able to directly detect a distance (range) toa target and a relative velocity thereof. Another characteristic is thatits detection performance is not much deteriorated in the nighttime(including dusk), or in bad weather, e.g., rainfall, fog, or snowfall.On the other hand, it is believed that it is not just as easy for amillimeter wave radar to take a two-dimensional grasp of a target as itis for a camera. On the other hand, it is relatively easy for a camerato take a two-dimensional grasp of a target and recognize its shape.However, a camera may not be able to image a target in nighttime or badweather, which presents a considerable problem. This problem isparticularly outstanding when droplets of water have adhered to theportion through which to ensure lighting, or the eyesight is narrowed bya fog. This problem similarly exists for LIDAR or the like, which alsopertains to the realm of optical sensors.

In these years, in answer to increasing demand for safer vehicleoperation, driver assist systems for preventing collisions or the likeare being developed. A driver assist system acquires an image in thedirection of vehicle travel with a sensor such as a camera or amillimeter wave radar, and when any obstacle is recognized that ispredicted to hinder vehicle travel, brakes or the like are automaticallyapplied to prevent collisions or the like. Such a function of collisionavoidance is expected to operate normally, even in nighttime or badweather.

Hence, driver assist systems of a so-called fusion construction aregaining prevalence, where, in addition to a conventional optical sensorsuch as a camera, a millimeter wave radar is mounted as a sensor, thusrealizing a recognition process that takes advantage of both. Such adriver assist system will be discussed later.

On the other hand, higher and higher functions are being required of themillimeter wave radar itself. A millimeter wave radar for onboard usemainly uses electromagnetic waves of the 76 GHz band. The antenna powerof its antenna is restricted to below a certain level under eachcountry's law or the like. For example, it is restricted to 0.01 W orbelow in Japan. Under such restrictions, a millimeter wave radar foronboard use is expected to satisfy the required performance that, forexample, its detection range is 200 m or more; the antenna size is 60mm×60 mm or less; its horizontal detection angle is 90 degrees or more;its range resolution is 20 cm or less; it is capable of short-rangedetection within 10 m; and so on. Conventional millimeter wave radarshave used microstrip lines as waveguides, and patch antennas as antennas(hereinafter, these will both be referred to as “patch antennas”).However, with a patch antenna, it has been difficult to attain theaforementioned performance.

By using a slot array antenna to which the technique of the presentdisclosure is applied, the inventors have successfully achieved theaforementioned performance. As a result, a millimeter wave radar hasbeen realized which is smaller in size, more efficient, andhigher-performance than are conventional patch antennas and the like. Inaddition, by combining this millimeter wave radar and an optical sensorsuch as a camera, a small-sized, highly efficient, and high-performancefusion apparatus has been realized which has existed never before. Thiswill be described in detail below.

FIG. 31 is a diagram concerning a fusion apparatus in a vehicle 500, thefusion apparatus including an onboard camera system 700 and a radarsystem 510 (hereinafter referred to also as the millimeter wave radar510) having a slot array antenna to which the technique of the presentdisclosure is applied. With reference to this figure, variousembodiments will be described below.

[Installment of Millimeter Wave Radar within Vehicle Room]

A conventional patch antenna-based millimeter wave radar 510′ is placedbehind and inward of a grill 512 which is at the front nose of avehicle. An electromagnetic wave that is radiated from an antenna goesthrough the apertures in the grill 512, and is radiated ahead of thevehicle 500. In this case, no dielectric layer, e.g., glass, exists thatdecays or reflects electromagnetic wave energy, in the region throughwhich the electromagnetic wave passes. As a result, an electromagneticwave that is radiated from the patch antenna-based millimeter wave radar510′ reaches over a long range, e.g., to a target which is 150 m orfarther away. By receiving with the antenna the electromagnetic wavereflected therefrom, the millimeter wave radar 510′ is able to detect atarget. In this case, however, since the antenna is placed behind andinward of the grill 512 of the vehicle, the radar may be broken when thevehicle collides into an obstacle. Moreover, it may be soiled with mudor the like in rain, etc., and the soil that has adhered to the antennamay hinder radiation and reception of electromagnetic waves.

Similarly to the conventional manner, the millimeter wave radar 510incorporating a slot array antenna according to an embodiment of thepresent disclosure may be placed behind the grill 512, which is locatedat the front nose of the vehicle (not shown). This allows the energy ofthe electromagnetic wave to be radiated from the antenna to be utilizedby 100%, thus enabling long-range detection beyond the conventionallevel, e.g., detection of a target which is at a distance of 250 m ormore.

Furthermore, the millimeter wave radar 510 according to an embodiment ofthe present disclosure can also be placed within the vehicle room, i.e.,inside the vehicle. In that case, the millimeter wave radar 510 isplaced inward of the windshield 511 of the vehicle, to fit in a spacebetween the windshield 511 and a face of the rearview mirror (not shown)that is opposite to its specular surface. On the other hand, theconventional patch antenna-based millimeter wave radar 510′ cannot beplaced inside the vehicle room mainly for the two following reasons. Afirst reason is its large size, which prevents itself from beingaccommodated within the space between the windshield 511 and therearview mirror. A second reason is that an electromagnetic wave that isradiated ahead reflects off the windshield 511 and decays due todielectric loss, thus becoming unable to travel the desired distance. Asa result, if a conventional patch antenna-based millimeter wave radar isplaced within the vehicle room, only targets which are 100 m ahead orless can be detected, for example. On the other hand, a millimeter waveradar according to an embodiment of the present disclosure is able todetect a target which is at a distance of 200 m or more, despitereflection or decay at the windshield 511. This performance isequivalent to, or even greater than, the case where a conventional patchantenna-based millimeter wave radar is placed outside the vehicle room.

[Fusion Construction Based on Millimeter Wave Radar and Camera, Etc.,being Placed within Vehicle Room]

Currently, an optical imaging device such as a CCD camera is used as themain sensor in many a driver assist system (Driver Assist System).Usually, a camera or the like is placed within the vehicle room, inwardof the windshield 511, in order to account for unfavorable influences ofthe external environment, etc. In this context, in order to minimize theoptical effect of raindrops and the like, the camera or the like isplaced in a region which is swept by the wipers (not shown) but isinward of the windshield 511.

In recent years, due to needs for improved performance of a vehicle interms of e.g. automatic braking, there has been a desire for automaticbraking or the like that is guaranteed to work regardless of whateverexternal environment may exist. In this case, if the only sensor in thedriver assist system is an optical device such as a camera, a problemexists in that reliable operation is not guaranteed in nighttime or badweather. This has led to the need for a driver assist system thatincorporates not only an optical sensor (such as a camera) but also amillimeter wave radar, these being used for cooperative processing, sothat reliable operation is achieved even in nighttime or bad weather.

As described earlier, a millimeter wave radar incorporating the presentslot array antenna permits itself to be placed within the vehicle room,due to downsizing and remarkable enhancement in the efficiency of theradiated electromagnetic wave over that of a conventional patch antenna.By taking advantage of these properties, as shown in FIG. 31, themillimeter wave radar 510, which incorporates not only an optical sensor(onboard camera system) 700 such as a camera but also a slot arrayantenna according to the present disclosure, allows both to be placedinward of the windshield 511 of the vehicle 500. This has created thefollowing novel effects.

(1) It is easier to install the driver assist system on the vehicle 500.The conventional patch antenna-based millimeter wave radar 510′ hasrequired a space behind the grill 512, which is at the front nose, inorder to accommodate the radar. Since this space may include some sitesthat affect the structural design of the vehicle, if the size of theradar device is changed, it may have been necessary to reconsider thestructural design. This inconvenience is avoided by placing themillimeter wave radar within the vehicle room.(2) Free from the influences of rain, nighttime, or other externalenvironment factors to the vehicle, more reliable operation can beachieved. Especially, as shown in FIG. 32, by placing the millimeterwave radar (onboard camera system) 510 and the onboard camera system 700at substantially the same position within the vehicle room, they canattain an identical field of view and line of sight, thus facilitatingthe “matching process” which will be described later, i.e., a processthrough which to establish that respective pieces of target informationcaptured by them actually come from an identical object. On the otherhand, if the millimeter wave radar 510′ were placed behind the grill512, which is at the front nose outside the vehicle room, its radar lineof sight L would differ from a radar line of sight M of the case whereit was placed within the vehicle room, thus resulting in a large offsetwith the image to be acquired by the onboard camera system 700.(3) Reliability of the millimeter wave radar device is improved. Asdescribed above, since the conventional patch antenna-based millimeterwave radar 510′ is placed behind the grill 512, which is at the frontnose, it is likely to gather soil, and may be broken even in a minorcollision accident or the like. For these reasons, cleaning andfunctionality checks are always needed. Moreover, as will be describedbelow, if the position or direction of attachment of the millimeter waveradar becomes shifted due to an accident or the like, it is necessary toreestablish alignment with respect to the camera. The chances of suchoccurrences are reduced by placing the millimeter wave radar within thevehicle room, whereby the aforementioned inconveniences are avoided.

In a driver assist system of such fusion construction, the opticalsensor, e.g., a camera, and the millimeter wave radar 510 incorporatingthe present slot array antenna may have an integrated construction,i.e., being in fixed position with respect to each other. In that case,certain relative positioning should be kept between the optical axis ofthe optical sensor such as a camera and the directivity of the antennaof the millimeter wave radar, as will be described later. When thisdriver assist system having an integrated construction is fixed withinthe vehicle room of the vehicle 500, the optical axis of the camera,etc., should be adjusted so as to be oriented in a certain directionahead of the vehicle. For these matters, see the specification of USPatent Application Publication No. 2015/0264230, the specification of USPatent Application Publication No. 2016/0264065, U.S. patent applicationSer. No. 15/248,141, U.S. patent application Ser. No. 15/248,149, andU.S. patent application Ser. No. 15/248,156, which are incorporatedherein by reference. Related techniques concerning the camera aredescribed in the specification of U.S. Pat. No. 7,355,524, and thespecification of U.S. Pat. No. 7,420,159, the entire disclosure of eachwhich is incorporated herein by reference.

Regarding placement of an optical sensor such as a camera and amillimeter wave radar within the vehicle room, see, for example, thespecification of U.S. Pat. No. 8,604,968, the specification of U.S. Pat.No. 8,614,640, and the specification of U.S. Pat. No. 7,978,122, theentire disclosure of each which is incorporated herein by reference.However, at the time when these patents were filed for, onlyconventional antennas with patch antennas were the known millimeter waveradars, and thus observation was not possible over sufficient distances.For example, the distance that is observable with a conventionalmillimeter wave radar is considered to be at most 100 m to 150 m.Moreover, when a millimeter wave radar is placed inward of thewindshield, the large radar size inconveniently blocks the driver'sfield of view, thus hindering safe driving. On the other hand, amillimeter wave radar incorporating a slot array antenna according to anembodiment of the present disclosure is capable of being placed withinthe vehicle room because of its small size and remarkable enhancement inthe efficiency of the radiated electromagnetic wave over that of aconventional patch antenna. This enables a long-range observation over200 m, while not blocking the driver's field of view.

[Adjustment of Position of Attachment Between Millimeter Wave Radar andCamera, Etc.]

In the processing under fusion construction (which hereinafter may bereferred to as a “fusion process”), it is desired that an image which isobtained with a camera or the like and the radar information which isobtained with the millimeter wave radar map onto the same coordinatesystem because, if they differ as to position and target size,cooperative processing between both will be hindered.

This involves adjustment from the following three standpoints.

(1) The optical axis of the camera or the like and the antennadirectivity of the millimeter wave radar must have a certain fixedrelationship.

It is required that the optical axis of the camera or the like and theantenna directivity of the millimeter wave radar are matched.Alternatively, a millimeter wave radar may include two or moretransmission antennas and two or more reception antennas, thedirectivities of these antennas being intentionally made different.Therefore, it is necessary to guarantee that at least a certain knownrelationship exists between the optical axis of the camera or the likeand the directivities of these antennas.

In the case where the camera or the like and the millimeter wave radarhave the aforementioned integrated construction, i.e., being in fixedposition to each other, the relative positioning between the camera orthe like and the millimeter wave radar stays fixed. Therefore, theaforementioned requirements are satisfied with respect to such anintegrated construction. On the other hand, in a conventional patchantenna or the like, where the millimeter wave radar is placed behindthe grill 512 of the vehicle 500, the relative positioning between themis usually to be adjusted according to (2) below.

(2) A certain fixed relationship exists between an image acquired withthe camera or the like and radar information of the millimeter waveradar in an initial state (e.g., upon shipment) of having been attachedto the vehicle.

The positions of attachment of the optical sensor such as a camera andthe millimeter wave radar 510 or 510′ on the vehicle 500 will finally bedetermined in the following manner. At a predetermined position 800ahead of the vehicle 500, a chart to serve as a reference or a targetwhich is subject to observation by the radar (which will hereinafter bereferred to as, respectively, a “reference chart” and a “referencetarget”, and collectively as the “benchmark”) is accurately positioned.This is observed with an optical sensor such as a camera or with themillimeter wave radar 510. The observation information regarding theobserved benchmark is compared against previously-stored shapeinformation or the like of the benchmark, and the current offsetinformation is quantitated. Based on this offset information, by atleast one of the following means, the positions of attachment of anoptical sensor such as a camera and the millimeter wave radar 510 or510′ are adjusted or corrected. Any other means may also be employedthat can provide similar results.

(i) Adjust the positions of attachment of the camera and the millimeterwave radar so that the benchmark will come at a midpoint between thecamera and the millimeter wave radar. This adjustment may be done byusing a jig or tool, etc., which is separately provided.(ii) Determine an offset amounts of the camera and the axis/directivityof the millimeter wave radar relative to the benchmark, and throughimage processing of the camera image and radar processing, correct forthese offset amounts in the axis/directivity.

What is to be noted is that, in the case where the optical sensor suchas a camera and the millimeter wave radar 510 incorporating a slot arrayantenna according to an embodiment of the present disclosure have anintegrated construction, i.e., being in fixed position to each other,adjusting an offset of either the camera or the radar with respect tothe benchmark will make the offset amount known for the other as well,thus making it unnecessary to check for the other's offset with respectto the benchmark.

Specifically, with respect to the onboard camera system 700, a referencechart may be placed at a predetermined position 750, and an image takenby the camera is compared against advance information indicating wherein the field of view of the camera the reference chart image is supposedto be located, thereby detecting an offset amount. Based on this, thecamera is adjusted by at least one of the above means (i) and (ii).Next, the offset amount which has been ascertained for the camera istranslated into an offset amount of the millimeter wave radar.Thereafter, an offset amount adjustment is made with respect to theradar information, by at least one of the above means (i) and (ii).

Alternatively, this may be performed on the basis of the millimeter waveradar 510. In other words, with respect to the millimeter wave radar510, a reference target may be placed at a predetermined position 800,and the radar information thereof is compared against advanceinformation indicating where in the field of view of the millimeter waveradar 510 the reference target is supposed to be located, therebydetecting an offset amount. Based on this, the millimeter wave radar 510is adjusted by at least one of the above means (i) and (ii). Next, theoffset amount which has been ascertained for the millimeter wave radaris translated into an offset amount of the camera. Thereafter, an offsetamount adjustment is made with respect to the image information obtainedby the camera, by at least one of the above means (i) and (ii).

(3) Even after an initial state of the vehicle, a certain relationshipis maintained between an image acquired with the camera or the like andradar information of the millimeter wave radar.

Usually, an image acquired with the camera or the like and radarinformation of the millimeter wave radar are supposed to be fixed in theinitial state, and hardly vary unless in an accident of the vehicle orthe like. However, if an offset in fact occurs between these, anadjustment is possible by the following means.

The camera is attached in such a manner that portions 513 and 514(characteristic points) that are characteristic of the driver's vehiclefit within its field of view, for example. The positions at which thesecharacteristic points are actually imaged by the camera are comparedagainst the information of the positions to be assumed by thesecharacteristic points when the camera is attached accurately in place,and an offset amount(s) is detected therebetween. Based on this detectedoffset amount(s), the position of any image that is taken thereafter maybe corrected, whereby an offset of the physical position of attachmentof the camera can be corrected for. If this correction sufficientlyembodies the performance that is required of the vehicle, then theadjustment per the above (2) may not be needed. By regularly performingthis adjustment during startup or operation of the vehicle 500, even ifan offset of the camera or the like occurs anew, it is possible tocorrect for the offset amount, thus helping safe travel.

However, this means is generally considered to result in poorer accuracyof adjustment than with the above means (2). When making an adjustmentbased on an image which is obtained by imaging a benchmark with thecamera, the azimuth of the benchmark can be determined with a highprecision, whereby a high accuracy of adjustment can be easily achieved.However, since this means utilizes a part of the vehicle body for theadjustment instead of a benchmark, it is rather difficult to enhance theaccuracy of azimuth determination. Thus, the resultant accuracy ofadjustment will be somewhat inferior. However, it may still3 beeffective as a means of correction when the position of attachment ofthe camera or the like is considerably altered for reasons such as anaccident or a large external force being applied to the camera or thelike within the vehicle room, etc.

[Mapping of Target as Detected by Millimeter Wave Radar and Camera orthe Like: Matching Process]

In a fusion process, for a given target, it needs to be established thatan image thereof which is acquired with a camera or the like and radarinformation which is acquired with the millimeter wave radar pertain to“the same target”. For example, suppose that two obstacles (first andsecond obstacles), e.g., two bicycles, have appeared ahead of thevehicle 500. These two obstacles will be captured as camera images, anddetected as radar information of the millimeter wave radar. At thistime, the camera image and the radar information with respect to thefirst obstacle need to be mapped to each other so that they are bothdirected to the same target. Similarly, the camera image and the radarinformation with respect to the second obstacle need to be mapped toeach other so that they are both directed to the same target. If thecamera image of the first obstacle and the radar information of thesecond obstacle are mistakenly recognized to pertain to an identicalobject, a considerable accident may occur. Hereinafter, in the presentspecification, such a process of determining whether a target in thecamera image and a target in the radar image pertain to the same targetmay be referred to as a “matching process”.

This matching process may be implemented by various detection devices(or methods) described below. Hereinafter, these will be specificallydescribed. Note that the each of the following detection devices is tobe installed in the vehicle, and at least includes a millimeter waveradar detection section, an image detection section (e.g., a camera)which is oriented in a direction overlapping the direction of detectionby the millimeter wave radar detection section, and a matching section.Herein, the millimeter wave radar detection section includes a slotarray antenna according to any of the embodiments of the presentdisclosure, and at least acquires radar information in its own field ofview. The image acquisition section at least acquires image informationin its own field of view. The matching section includes a processingcircuit which matches a result of detection by the millimeter wave radardetection section against a result of detection by the image detectionsection to determine whether or not the same target is being detected bythe two detection sections. Herein, the image detection section may becomposed of a selected one of, or selected two or more of, an opticalcamera, LIDAR, an infrared radar, and an ultrasonic radar. The followingdetection devices differ from one another in terms of the detectionprocess at their respective matching section.

In a first detection device, the matching section performs two matchesas follows. A first match involves, for a target of interest that hasbeen detected by the millimeter wave radar detection section, obtainingdistance information and lateral position information thereof, and alsofinding a target that is the closest to the target of interest among atarget or two or more targets detected by the image detection section,and detecting a combination(s) thereof. A second match involves, for atarget of interest that has been detected by the image detectionsection, obtaining distance information and lateral position informationthereof, and also finding a target that is the closest to the target ofinterest among a target or two or more targets detected by themillimeter wave radar detection section, and detecting a combination(s)thereof. Furthermore, this matching section determines whether there isany matching combination between the combination(s) of such targets asdetected by the millimeter wave radar detection section and thecombination(s) of such targets as detected by the image detectionsection. Then, if there is any matching combination, it is determinedthat the same object is being detected by the two detection sections. Inthis manner, a match is attained between the respective targets thathave been detected by the millimeter wave radar detection section andthe image detection section.

A related technique is described in the specification of U.S. Pat. No.7,358,889, the entire disclosure of which is incorporated herein byreference. In this publication, the image detection section isillustrated by way of a so-called stereo camera that includes twocameras. However, this technique is not limited thereto. In the casewhere the image detection section includes a single camera, detectedtargets may be subjected to an image recognition process or the like asappropriate, in order to obtain distance information and lateralposition information of the targets. Similarly, a laser sensor such as alaser scanner may be used as the image detection section.

In a second detection device, the matching section matches a result ofdetection by the millimeter wave radar detection section and a result ofdetection by the image detection section every predetermined period oftime. If the matching section determines that the same target was beingdetected by the two detection sections in the previous result ofmatching, it performs a match by using this previous result of matching.Specifically, the matching section matches a target which is currentlydetected by the millimeter wave radar detection section and a targetwhich is currently detected by the image detection section, against thetarget which was determined in the previous result of matching to bebeing detected by the two detection sections. Then, based on the resultof matching for the target which is currently detected by the millimeterwave radar detection section and the result of matching for the targetwhich is currently detected by the image detection section, the matchingsection determines whether or not the same target is being detected bythe two detection sections. Thus, rather than directly matching theresults of detection by the two detection sections, this detectiondevice performs a chronological match between the two results ofdetection and a previous result of matching. Therefore, the accuracy ofdetection is improved over the case of only performing a momentarymatch, whereby stable matching is realized. In particular, even if theaccuracy of the detection section drops momentarily, matching is stillpossible because of utilizing past results of matching. Moreover, byutilizing the previous result of matching, this detection device is ableto easily perform a match between the two detection sections.

In the current match which utilizes the previous result of matching, ifthe matching section of this detection device determines that the sameobject is being detected by the two detection sections, then thematching section of this detection device excludes this determinedobject in performing matching between objects which are currentlydetected by the millimeter wave radar detection section and objectswhich are currently detected by the image detection section. Then, thismatching section determines whether there exists any identical objectthat is currently detected by the two detection sections. Thus, whiletaking into account the result of chronological matching, the detectiondevice also makes a momentary match based on two results of detectionthat are obtained from moment to moment. As a result, the detectiondevice is able to surely perform a match for any object that is detectedduring the current detection.

A related technique is described in the specification of U.S. Pat. No.7,417,580, the entire disclosure of which is incorporated herein byreference. In this publication, the image detection section isillustrated by way of a so-called stereo camera that includes twocameras. However, this technique is not limited thereto. In the casewhere the image detection section includes a single camera, detectedtargets may be subjected to an image recognition process or the like asappropriate, in order to obtain distance information and lateralposition information of the targets. Similarly, a laser sensor such as alaser scanner may be used as the image detection section.

In a third detection device, the two detection sections and matchingsection perform detection of targets and performs matches therebetweenat predetermined time intervals, and the results of such detection andthe results of such matching are chronologically stored to a storagemedium, e.g., memory. Then, based on a rate of change in the size of atarget in the image as detected by the image detection section, and on adistance to a target from the driver's vehicle and its rate of change(relative velocity with respect to the driver's vehicle) as detected bythe millimeter wave radar detection section, the matching sectiondetermines whether the target which has been detected by the imagedetection section and the target which has been detected by themillimeter wave radar detection section are an identical object.

When determining that these targets are an identical object, based onthe position of the target in the image as detected by the imagedetection section, and on the distance to the target from the driver'svehicle and/or its rate of change as detected by the millimeter waveradar detection section, the matching section predicts a possibility ofcollision with the vehicle.

A related technique is described in the specification of U.S. Pat. No.6,903,677, the entire disclosure of which is incorporated herein byreference.

As described above, in a fusion process of a millimeter wave radar andan imaging device such as a camera, an image which is obtained with thecamera or the like and radar information which is obtained with themillimeter wave radar are matched against each other. A millimeter waveradar incorporating the aforementioned array antenna according to anembodiment of the present disclosure can be constructed so as to have asmall size and high performance. Therefore, high performance anddownsizing, etc., can be achieved for the entire fusion processincluding the aforementioned matching process. This improves theaccuracy of target recognition, and enables safer travel control for thevehicle.

[Other Fusion Processes]

In a fusion process, various functions are realized based on a matchingprocess between an image which is obtained with a camera or the like andradar information which is obtained with the millimeter wave radardetection section. Examples of processing apparatuses that realizerepresentative functions of a fusion process will be described below.

Each of the following processing apparatuses is to be installed in avehicle, and at least includes: a millimeter wave radar detectionsection to transmit or receive electromagnetic waves in a predetermineddirection; an image acquisition section, such as a monocular camera,that has a field of view overlapping the field of view of the millimeterwave radar detection section; and a processing section which obtainsinformation therefrom to perform target detection and the like. Themillimeter wave radar detection section acquires radar information inits own field of view. The image acquisition section acquires imageinformation in its own field of view. A selected one, or selected two ormore of, an optical camera, LIDAR, an infrared radar, and an ultrasonicradar may be used as the image acquisition section. The processingsection can be implemented by a processing circuit which is connected tothe millimeter wave radar detection section and the image acquisitionsection. The following processing apparatuses differ from one anotherwith respect to the content of processing by this processing section.

In a first processing apparatus, the processing section extracts, froman image which is captured by the image acquisition section, a targetwhich is recognized to be the same as the target which is detected bythe millimeter wave radar detection section. In other words, a matchingprocess according to the aforementioned detection device is performed.Then, it acquires information of a right edge and a left edge of theextracted target image, and derives locus approximation lines, which arestraight lines or predetermined curved lines for approximating loci ofthe acquired right edge and the left edge, are derived for both edges.The edge which has a larger number of edges existing on the locusapproximation line is selected as a true edge of the target. The lateralposition of the target is derived on the basis of the position of theedge that has been selected as a true edge. This permits a furtherimprovement on the accuracy of detection of a lateral position of thetarget.

A related technique is described in the specification of U.S. Pat. No.8,610,620, the entire disclosure of which is incorporated herein byreference.

In a second processing apparatus, in determining the presence of atarget, the processing section alters a determination threshold to beused in checking for a target presence in radar information, on thebasis of image information. Thus, if a target image that may be anobstacle to vehicle travel has been confirmed with a camera or the like,or if the presence of a target has been estimated, etc., for example,the determination threshold for the target detection by the millimeterwave radar detection section can be optimized so that more accuratetarget information can be obtained. In other words, if the possibilityof the presence of an obstacle is high, the determination threshold isaltered so that this processing apparatus will surely be activated. Onthe other hand, if the possibility of the presence of an obstacle islow, the determination threshold is altered so that unwanted activationof this processing apparatus is prevented. This permits appropriateactivation of the system.

Furthermore in this case, based on radar information, the processingsection may designate a region of detection for the image information,and estimate a possibility of the presence of an obstacle on the basisof image information within this region. This makes for a more efficientdetection process.

A related technique is described in the specification of U.S. Pat. No.7,570,198, the entire disclosure of which is incorporated herein byreference.

In a third processing apparatus, the processing section performscombined displaying where images obtained from a plurality of differentimaging devices and a millimeter wave radar detection section and animage signal based on radar information are displayed on at least onedisplay device. In this displaying process, horizontal and verticalsynchronizing signals are synchronized between the plurality of imagingdevices and the millimeter wave radar detection section, and among theimage signals from these devices, selective switching to a desired imagesignal is possible within one horizontal scanning period or one verticalscanning period. This allows, on the basis of the horizontal andvertical synchronizing signals, images of a plurality of selected imagesignals to be displayed side by side; and, from the display device, acontrol signal for setting a control operation in the desired imagingdevice and the millimeter wave radar detection section is sent.

When a plurality of different display devices display respective imagesor the like, it is difficult to compare the respective images againstone another. Moreover, when display devices are provided separately fromthe third processing apparatus itself, there is poor operability for thedevice. The third processing apparatus would overcome such shortcomings.

A related technique is described in the specification of U.S. Pat. No.6,628,299 and the specification of U.S. Pat. No. 7,161,561, the entiredisclosure of each of which is incorporated herein by reference.

In a fourth processing apparatus, with respect to a target which isahead of a vehicle, the processing section instructs an imageacquisition section and a millimeter wave radar detection section toacquire an image and radar information containing that target. Fromwithin such image information, the processing section determines aregion in which the target is contained. Furthermore, the processingsection extracts radar information within this region, and detects adistance from the vehicle to the target and a relative velocity betweenthe vehicle and the target. Based on such information, the processingsection determines a possibility that the target will collide againstthe vehicle. This enables an early detection of a possible collisionwith a target.

A related technique is described in the specification of U.S. Pat. No.8,068,134, the entire disclosure of which is incorporated herein byreference.

In a fifth processing apparatus, based on radar information or through afusion process which is based on radar information and imageinformation, the processing section recognizes a target or two or moretargets ahead of the vehicle. The “target” encompasses any moving entitysuch as other vehicles or pedestrians, traveling lanes indicated bywhite lines on the road, road shoulders and any still objects (includinggutters, obstacles, etc.), traffic lights, pedestrian crossings, and thelike that may be there. The processing section may encompass a GPS(Global Positioning System) antenna. By using a GPS antenna, theposition of the driver's vehicle may be detected, and based on thisposition, a storage device (referred to as a map information databasedevice) that stores road map information may be searched in order toascertain a current position on the map. This current position on themap may be compared against a target or two or more targets that havebeen recognized based on radar information or the like, whereby thetraveling environment may be recognized. On this basis, the processingsection may extract any target that is estimated to hinder vehicletravel, find safer traveling information, and display it on a displaydevice, as necessary, to inform the driver.

A related technique is described in the specification of U.S. Pat. No.6,191,704, the entire disclosure of which is incorporated herein byreference.

The fifth processing apparatus may further include a data communicationdevice (having communication circuitry) that communicates with a mapinformation database device which is external to the vehicle. The datacommunication device may access the map information database device,with a period of e.g. once a week or once a month, to download thelatest map information therefrom. This allows the aforementionedprocessing to be performed with the latest map information.

Furthermore, the fifth processing apparatus may compare between thelatest map information that was acquired during the aforementionedvehicle travel and information that is recognized of a target or two ormore targets based on radar information, etc., in order to extracttarget information (hereinafter referred to as “map update information”)that is not included in the map information. Then, this map updateinformation may be transmitted to the map information database devicevia the data communication device. The map information database devicemay store this map update information in association with the mapinformation that is within the database, and update the current mapinformation itself, if necessary. In performing the update, respectivepieces of map update information that are obtained from a plurality ofvehicles may be compared against one another to check certainty of theupdate.

Note that this map update information may contain more detailedinformation than the map information which is carried by any currentlyavailable map information database device. For example, schematic shapesof roads may be known from commonly-available map information, but ittypically does not contain information such as the width of the roadshoulder, the width of the gutter that may be there, any newly occurringbumps or dents, shapes of buildings, and so on. Neither does it containheights of the roadway and the sidewalk, how a slope may connect to thesidewalk, etc. Based on conditions which are separately set, the mapinformation database device may store such detailed information(hereinafter referred to as “map update details information”) inassociation with the map information. Such map update detailsinformation provides a vehicle (including the driver's vehicle) withinformation which is more detailed than the original map information,thereby rending itself available for not only the purpose of ensuringsafe vehicle travel but also some other purposes. As used herein, a“vehicle (including the driver's vehicle)” may be e.g. an automobile, amotorcycle, a bicycle, or any autonomous vehicle to become available inthe future, e.g., an electric wheelchair. The map update detailsinformation is to be used when any such vehicle may travel.

(Recognition Via Neural Network)

Each of the first to fifth processing apparatuses may further include asophisticated apparatus of recognition. The sophisticated apparatus ofrecognition may be provided external to the vehicle. In that case, thevehicle may include a high-speed data communication device thatcommunicates with the sophisticated apparatus of recognition. Thesophisticated apparatus of recognition may be constructed from a neuralnetwork, which may encompass so-called deep learning and the like. Thisneural network may include a convolutional neural network (hereinafterreferred to as “CNN”), for example. A CNN, a neural network that hasproven successful in image recognition, is characterized by possessingone or more sets of two layers, namely, a convolutional layer and apooling layer.

There exists at least three kinds of information as follows, any ofwhich may be input to a convolutional layer in the processing apparatus:

(1) information that is based on radar information which is acquired bythe millimeter wave radar detection section;

(2) information that is based on specific image information which isacquired, based on radar information, by the image acquisition section;or

(3) fusion information that is based on radar information and imageinformation which is acquired by the image acquisition section, orinformation that is obtained based on such fusion information.

Based on information of any of the above kinds, or information based ona combination thereof, product-sum operations corresponding to aconvolutional layer are performed. The results are input to thesubsequent pooling layer, where data is selected according to apredetermined rule. In the case of max pooling where a maximum valueamong pixel values is chosen, for example, the rule may dictate that amaximum value be chosen for each split region in the convolutionallayer, this maximum value being regarded as the value of thecorresponding position in the pooling layer.

A sophisticated apparatus of recognition that is composed of a CNN mayinclude a single set of a convolutional layer and a pooling layer, or aplurality of such sets which are cascaded in series. This enablesaccurate recognition of a target, which is contained in the radarinformation and the image information, that may be around a vehicle.

Related techniques are described in the U.S. Pat. No. 8,861,842, thespecification of U.S. Pat. No. 9,286,524, and the specification of USPatent Application Publication No. 2016/0140424, the entire disclosureof each of which is incorporated herein by reference.

In a sixth processing apparatus, the processing section performsprocessing that is related to headlamp control of a vehicle. When avehicle travels in nighttime, the driver may check whether anothervehicle or a pedestrian exists ahead of the driver's vehicle, andcontrol a beam(s) from the headlamp(s) of the driver's vehicle toprevent the driver of the other vehicle or the pedestrian from beingdazzled by the headlamp(s) of the driver's vehicle. This sixthprocessing apparatus automatically controls the headlamp(s) of thedriver's vehicle by using radar information, or a combination of radarinformation and an image taken by a camera or the like.

Based on radar information, or through a fusion process based on radarinformation and image information, the processing section detects atarget that corresponds to a vehicle or pedestrian ahead of the vehicle.In this case, a vehicle ahead of a vehicle may encompass a precedingvehicle that is ahead, a vehicle or a motorcycle in the oncoming lane,and so on. When detecting any such target, the processing section issuesa command to lower the beam(s) of the headlamp(s). Upon receiving thiscommand, the control section (control circuit) which is internal to thevehicle may control the headlamp(s) to lower the beam(s) therefrom.

Related techniques are described in the specification of U.S. Pat. No.6,403,942, the specification of U.S. Pat. No. 6,611,610, thespecification of U.S. Pat. No. 8,543,277, the specification of U.S. Pat.No. 8,593,521, and the specification of U.S. Pat. No. 8,636,393, theentire disclosure of each of which is incorporated herein by reference.

According to the above-described processing by the millimeter wave radardetection section, and the above-described fusion process by themillimeter wave radar detection section and an imaging device such as acamera, the millimeter wave radar can be constructed so as to have asmall size and high performance, whereby high performance anddownsizing, etc., can be achieved for the radar processing or the entirefusion process. This improves the accuracy of target recognition, andenables safer travel control for the vehicle.

Application Example 2: Various Monitoring Systems (Natural Elements,Buildings, Roads, Watch, Security)

A millimeter wave radar (radar system) incorporating an array antennaaccording to an embodiment of the present disclosure also has a widerange of applications in the fields of monitoring, which may encompassnatural elements, weather, buildings, security, nursing care, and thelike. In a monitoring system in this context, a monitoring apparatusthat includes the millimeter wave radar may be installed e.g. at a fixedposition, in order to perpetually monitor a subject(s) of monitoring.Regarding the given subject(s) of monitoring, the millimeter wave radarhas its resolution of detection adjusted and set to an optimum value.

A millimeter wave radar incorporating an array antenna according to anembodiment of the present disclosure is capable of detection with aradio frequency electromagnetic wave exceeding e.g. 100 GHz. As for themodulation band in those schemes which are used in radar recognition,e.g., the FMCW method, the millimeter wave radar currently achieves awide band exceeding 4 GHz, which supports the aforementioned Ultra WideBand (UWB). Note that the modulation band is related to the rangeresolution. In a conventional patch antenna, the modulation band was upto about 600 MHz, thus resulting in a range resolution of 25 cm. On theother hand, a millimeter wave radar associated with the present arrayantenna has a range resolution of 3.75 cm, indicative of a performancewhich rivals the range resolution of conventional LIDAR. Whereas anoptical sensor such as LIDAR is unable to detect a target in nighttimeor bad weather as mentioned above, a millimeter wave radar is alwayscapable of detection, regardless of daytime or nighttime andirrespective of weather. As a result, a millimeter wave radar associatedwith the present array antenna is available for a variety ofapplications which were not possible with a millimeter wave radarincorporating any conventional patch antenna.

FIG. 33 is a diagram showing an exemplary construction for a monitoringsystem 1500 based on millimeter wave radar. The monitoring system 1500based on millimeter wave radar at least includes a sensor section 1010and a main section 1100. The sensor section 1010 at least includes anantenna 1011 which is aimed at the subject of monitoring 1015, amillimeter wave radar detection section 1012 which detects a targetbased on a transmitted or received electromagnetic wave, and acommunication section (communication circuit) 1013 which transmitsdetected radar information. The main section 1100 at least includes acommunication section (communication circuit) 1103 which receives radarinformation, a processing section (processing circuit) 1101 whichperforms predetermined processing based on the received radarinformation, and a data storage section (storage medium) 1102 in whichpast radar information and other information that is needed for thepredetermined processing, etc., are stored. Telecommunication lines 1300exist between the sensor section 1010 and the main section 1100, viawhich transmission and reception of information and commands occurbetween them. As used herein, the telecommunication lines may encompassany of a general-purpose communications network such as the Internet, amobile communications network, dedicated telecommunication lines, and soon, for example. Note that the present monitoring system 1500 may bearranged so that the sensor section 1010 and the main section 1100 aredirectly connected, rather than via telecommunication lines. In additionto the millimeter wave radar, the sensor section 1010 may also includean optical sensor such as a camera. This will permit target recognitionthrough a fusion process which is based on radar information and imageinformation from the camera or the like, thus enabling a moresophisticated detection of the subject of monitoring 1015 or the like.

Hereinafter, examples of monitoring systems embodying these applicationswill be specifically described.

[Natural Element Monitoring System]

A first monitoring system is a system that monitors natural elements(hereinafter referred to as a “natural element monitoring system”). Withreference to FIG. 33, this natural element monitoring system will bedescribed. Subjects of monitoring 1015 of the natural element monitoringsystem 1500 may be, for example, a river, the sea surface, a mountain, avolcano, the ground surface, or the like. For example, when a river isthe subject of monitoring 1015, the sensor section 1010 being secured toa fixed position perpetually monitors the water surface of the river1015. This water surface information is perpetually transmitted to aprocessing section 1101 in the main section 1100. Then, if the watersurface reaches a certain height or above, the processing section 1101informs a distinct system 1200 which separately exists from themonitoring system (e.g., a weather observation monitoring system), viathe telecommunication lines 1300. Alternatively, the processing section1101 may send information to a system (not shown) which manages thewater gate, whereby the system if instructed to automatically close awater gate, etc. (not shown) which is provided at the river 1015.

The natural element monitoring system 1500 is able to monitor aplurality of sensor sections 1010, 1020, etc., with the single mainsection 1100. When the plurality of sensor sections are distributed overa certain area, the water levels of rivers in that area can be graspedsimultaneously. This allows to make an assessment as to how the rainfallin this area may affect the water levels of the rivers, possibly leadingto disasters such as floods. Information concerning this can be conveyedto the distinct system 1200 (e.g., a weather observation monitoringsystem) via the telecommunication lines 1300. Thus, the distinct system1200 (e.g., a weather observation monitoring system) is able to utilizethe conveyed information for weather observation or disaster predictionin a wider area.

The natural element monitoring system 1500 is also similarly applicableto any natural element other than a river. For example, the subject ofmonitoring of a monitoring system that monitors tsunamis or storm surgesis the sea surface level. It is also possible to automatically open orclose the water gate of a seawall in response to a rise in the seasurface level. Alternatively, the subject of monitoring of a monitoringsystem that monitors landslides to be caused by rainfall, earthquakes,or the like may be the ground surface of a mountainous area, etc.

[Traffic Monitoring System]

A second monitoring system is a system that monitors traffic(hereinafter referred to as a “traffic monitoring system”). The subjectof monitoring of this traffic monitoring system may be, for example, arailroad crossing, a specific railroad, an airport runway, a roadintersection, a specific road, a parking lot, etc.

For example, when the subject of monitoring is a railroad crossing, thesensor section 1010 is placed at a position where the inside of thecrossing can be monitored. In this case, in addition to the millimeterwave radar, the sensor section 1010 may also include an optical sensorsuch as a camera, which will allow a target (subject of monitoring) tobe detected from more perspectives, through a fusion process based onradar information and image information. The target information which isobtained with the sensor section 1010 is sent to the main section 1100via the telecommunication lines 1300. The main section 1100 collectsother information (e.g., train schedule information) that may be neededin a more sophisticated recognition process or control, and issuesnecessary control instructions or the like based thereon. As usedherein, a necessary control instruction may be, for example, aninstruction to stop a train when a person, a vehicle, etc. is foundinside the crossing when it is closed.

If the subject of monitoring is a runway at an airport, for example, aplurality of sensor sections 1010, 1020, etc., may be placed along therunway so as to set the runway to a predetermined resolution, e.g., aresolution that allows any foreign object on the runway that is 5 cm by5 cm or larger to be detected. The monitoring system 1500 perpetuallymonitors the runway, regardless of daytime or nighttime and irrespectiveof weather. This function is enabled by the very ability of themillimeter wave radar according to an embodiment of the presentdisclosure to support UWB. Moreover, since the present millimeter waveradar device can be embodied with a small size, a high resolution, and alow cost, it provides a realistic solution for covering the entirerunway surface from end to end. In this case, the main section 1100keeps the plurality of sensor sections 1010, 1020, etc., underintegrated management. If a foreign object is found on the runway, themain section 1100 transmits information concerning the position and sizeof the foreign object to an air-traffic control system (not shown). Uponreceiving this, the air-traffic control system temporarily prohibitstakeoff and landing on that runway. In the meantime, the main section1100 transmits information concerning the position and size of theforeign object to a separately-provided vehicle, which automaticallycleans the runway surface, etc., for example. Upon receive this, thecleaning vehicle may autonomously move to the position where the foreignobject exists, and automatically remove the foreign object. Once removalof the foreign object is completed, the cleaning vehicle transmitsinformation of the completion to the main section 1100. Then, the mainsection 1100 again confirms that the sensor section 1010 or the likewhich has detected the foreign object now reports that “no foreignobject exists” and that it is safe now, and informs the air-trafficcontrol system of this. Upon receiving this, the air-traffic controlsystem may lift the prohibition of takeoff and landing from the runway.

Furthermore, in the case where the subject of monitoring is a parkinglot, for example, it may be possible to automatically recognize whichposition in the parking lot is currently vacant. A related technique isdescribed in the specification of U.S. Pat. No. 6,943,726, the entiredisclosure of which is incorporated herein by reference.

[Security Monitoring System]

A third monitoring system is a system that monitors a trespasser into apiece of private land or a house (hereinafter referred to as a “securitymonitoring system”). The subject of monitoring of this securitymonitoring system may be, for example, a specific region within a pieceof private land or a house, etc.

For example, if the subject of monitoring is a piece of private land,the sensor section(s) 1010 may be placed at one position, or two or morepositions where the sensor section(s) 1010 is able to monitor it. Inthis case, in addition to the millimeter wave radar, the sensorsection(s) 1010 may also include an optical sensor such as a camera,which will allow a target (subject of monitoring) to be detected frommore perspectives, through a fusion process based on radar informationand image information. The target information which was obtained by thesensor section 1010(s) is sent to the main section 1100 via thetelecommunication lines 1300. The main section 1100 collects otherinformation (e.g., reference data or the like needed to accuratelyrecognize whether the trespasser is a person or an animal such as a dogor a bird) that may be needed in a more sophisticated recognitionprocess or control, and issues necessary control instructions or thelike based thereon. As used herein, a necessary control instruction maybe, for example, an instruction to sound an alarm or activate lightingthat is installed in the premises, and also an instruction to directlyreport to a person in charge of the premises via mobiletelecommunication lines or the like, etc. The processing section 1101 inthe main section 1100 may allow an internalized, sophisticated apparatusof recognition (that adopts deep learning or a like technique) torecognize the detected target. Alternatively, such a sophisticatedapparatus of recognition may be provided externally, in which case thesophisticated apparatus of recognition may be connected via thetelecommunication lines 1300.

A related technique is described in the specification of U.S. Pat. No.7,425,983, the entire disclosure of which is incorporated herein byreference.

Another embodiment of such a security monitoring system may be a humanmonitoring system to be installed at a boarding gate at an airport, astation wicket, an entrance of a building, or the like. The subject ofmonitoring of such a human monitoring system may be, for example, aboarding gate at an airport, a station wicket, an entrance of abuilding, or the like.

If the subject of monitoring is a boarding gate at an airport, thesensor section(s) 1010 may be installed in a machine for checkingpersonal belongings at the boarding gate, for example. In this case,there may be two checking methods as follows. In a first method, themillimeter wave radar transmits an electromagnetic wave, and receivesthe electromagnetic wave as it reflects off a passenger (which is thesubject of monitoring), thereby checking personal belongings or the likeof the passenger. In a second method, a weak millimeter wave which isradiated from the passenger's own body is received by the antenna, thuschecking for any foreign object that the passenger may be hiding. In thelatter method, the millimeter wave radar preferably has a function ofscanning the received millimeter wave. This scanning function may beimplemented by using digital beam forming, or through a mechanicalscanning operation. Note that the processing by the main section 1100may utilize a communication process and a recognition process similar tothose in the above-described examples.

[Building Inspection System (Non-Destructive Inspection)]

A fourth monitoring system is a system that monitors or checks theconcrete material of a road, a railroad overpass, a building, etc., orthe interior of a road or the ground, etc., (hereinafter referred to asa “building inspection system”). The subject of monitoring of thisbuilding inspection system may be, for example, the interior of theconcrete material of an overpass or a building, etc., or the interior ofa road or the ground, etc.

For example, if the subject of monitoring is the interior of a concretebuilding, the sensor section 1010 is structured so that the antenna 1011can make scan motions along the surface of a concrete building. As usedherein, “scan motions” may be implemented manually, or a stationary railfor the scan motion may be separately provided, upon which to cause themovement by using driving power from an electric motor or the like. Inthe case where the subject of monitoring is a road or the ground, theantenna 1011 may be installed face-down on a vehicle or the like, andthe vehicle may be allowed to travel at a constant velocity, thuscreating a “scan motion”. The electromagnetic wave to be used by thesensor section 1010 may be a millimeter wave in e.g. the so-calledterahertz region, exceeding 100 GHz. As described earlier, even with anelectromagnetic wave over e.g. 100 GHz, an array antenna according to anembodiment of the present disclosure can be adapted to have smallerlosses than do conventional patch antennas or the like. Anelectromagnetic wave of a higher frequency is able to permeate deeperinto the subject of checking, such as concrete, thereby realizing a moreaccurate non-destructive inspection. Note that the processing by themain section 1100 may also utilize a communication process and arecognition process similar to those in the other monitoring systemsdescribed above.

A related technique is described in the specification of U.S. Pat. No.6,661,367, the entire disclosure of which is incorporated herein byreference.

[Human Monitoring System]

A fifth monitoring system is a system that watches over a person who issubject to nursing care (hereinafter referred to as a “human watchsystem”). The subject of monitoring of this human watch system may be,for example, a person under nursing care or a patient in a hospital,etc.

For example, if the subject of monitoring is a person under nursing carewithin a room of a nursing care facility, the sensor section(s) 1010 isplaced at one position, or two or more positions inside the room wherethe sensor section(s) 1010 is able to monitor the entirety of the insideof the room. In this case, in addition to the millimeter wave radar, thesensor section 1010 may also include an optical sensor such as a camera.In this case, the subject of monitoring can be monitored from moreperspectives, through a fusion process based on radar information andimage information. On the other hand, when the subject of monitoring isa person, from the standpoint of privacy protection, monitoring with acamera or the like may not be appropriate. Therefore, sensor selectionsmust be made while taking this aspect into consideration. Note thattarget detection by the millimeter wave radar will allow a person, whois the subject of monitoring, to be captured not by his or her image,but by a signal (which is, as it were, a shadow of the person).Therefore, the millimeter wave radar may be considered as a desirablesensor from the standpoint of privacy protection.

Information of the person under nursing care which has been obtained bythe sensor section(s) 1010 is sent to the main section 1100 via thetelecommunication lines 1300. The main section 1100 collects otherinformation (e.g., reference data or the like needed to accuratelyrecognize target information of the person under nursing care) that maybe needed in a more sophisticated recognition process or control, andissues necessary control instructions or the like based thereon. As usedherein, a necessary control instruction may be, for example, aninstruction to directly report a person in charge based on the result ofdetection, etc. The processing section 1101 in the main section 1100 mayallow an internalized, sophisticated apparatus of recognition (thatadopts deep learning or a like technique) to recognize the detectedtarget. Alternatively, such a sophisticated apparatus of recognition maybe provided externally, in which case the sophisticated apparatus ofrecognition may be connected via the telecommunication lines 1300.

In the case where a person is the subject of monitoring of themillimeter wave radar, at least the two following functions may beadded.

A first function is a function of monitoring the heart rate and/or therespiratory rate. In the case of a millimeter wave radar, anelectromagnetic wave is able to see through the clothes to detect theposition and motions of the skin surface of a person's body. First, theprocessing section 1101 detects a person who is the subject ofmonitoring and an outer shape thereof. Next, in the case of detecting aheart rate, for example, a position on the body surface where theheartbeat motions are easy to detect may be identified, and the motionsthere may be chronologically detected. This allows a heart rate perminute to be detected, for example. The same is also true when detectinga respiratory rate. By using this function, the health status of aperson under nursing care can be perpetually checked, thus enabling ahigher-quality watch over a person under nursing care.

A second function is a function of fall detection. A person undernursing care such as an elderly person may fall from time to time, dueto weakened legs and feet. When a person falls, the velocity oracceleration of a specification site of the person's body, e.g., thehead, will reach a certain level or greater. When the subject ofmonitoring of the millimeter wave radar is a person, the relativevelocity or acceleration of the target of interest can be perpetuallydetected. Therefore, by identifying the head as the subject ofmonitoring, for example, and chronologically detecting its relativevelocity or acceleration, a fall can be recognized when a velocity of acertain value or greater is detected. When recognizing a fall, theprocessing section 1101 can issue an instruction or the likecorresponding to pertinent nursing care assistance, for example.

Note that the sensor section(s) 1010 is secured to a fixed position(s)in the above-described monitoring system or the like. However, thesensor section(s) 1010 can also be installed on a moving entity, e.g., arobot, a vehicle, a flying object such as a drone. As used herein, thevehicle or the like may encompass not only an automobile, but also asmaller sized moving entity such as an electric wheelchair, for example.In this case, this moving entity may include an internal GPS unit whichallows its own current position to be always confirmed. In addition,this moving entity may also have a function of further improving theaccuracy of its own current position by using map information and themap update information which has been described with respect to theaforementioned fifth processing apparatus.

Furthermore, in any device or system that is similar to theabove-described first to third detection devices, first to sixthprocessing apparatuses, first to fifth monitoring systems, etc., a likeconstruction may be adopted to utilize an array antenna or a millimeterwave radar according to an embodiment of the present disclosure.

Application Example 3: Communication System First Example ofCommunication System

The waveguide device and antenna device (array antenna) according to thepresent disclosure can be used for the transmitter and/or receiver withwhich a communication system (telecommunication system) is constructed.The waveguide device and antenna device according to the presentdisclosure are composed of layered conductive members, and therefore areable to keep the transmitter and/or receiver size smaller than in thecase of using a hollow waveguide. Moreover, there is no need fordielectric, and thus the dielectric loss of electromagnetic waves can bekept smaller than in the case of using a microstrip line. Therefore, acommunication system including a small and highly efficient transmitterand/or receiver can be constructed.

Such a communication system may be an analog type communication systemwhich transmits or receives an analog signal that is directly modulated.However, a digital communication system may be adopted in order toconstruct a more flexible and higher-performance communication system.

Hereinafter, with reference to FIG. 34, a digital communication system800A in which a waveguide device and an antenna device according to anembodiment of the present disclosure are used will be described.

FIG. 34 is a block diagram showing a construction for the digitalcommunication system 800A. The communication system 800A includes atransmitter 810A and a receiver 820A. The transmitter 810A includes ananalog to digital (A/D) converter 812, an encoder 813, a modulator 814,and a transmission antenna 815. The receiver 820A includes a receptionantenna 825, a demodulator 824, a decoder 823, and a digital to analog(D/A) converter 822. The at least one of the transmission antenna 815and the reception antenna 825 may be implemented by using an arrayantenna according to an embodiment of the present disclosure. In thisexemplary application, the circuitry including the modulator 814, theencoder 813, the A/D converter 812, and so on, which are connected tothe transmission antenna 815, is referred to as the transmissioncircuit. The circuitry including the demodulator 824, the decoder 823,the D/A converter 822, and so on, which are connected to the receptionantenna 825, is referred to as the reception circuit. The transmissioncircuit and the reception circuit may be collectively referred to as thecommunication circuit.

With the analog to digital (A/D) converter 812, the transmitter 810Aconverts an analog signal which is received from the signal source 811to a digital signal. Next, the digital signal is encoded by the encoder813. As used herein, “encoding” means altering the digital signal to betransmitted into a format which is suitable for communication. Examplesof such encoding include CDM (Code-Division Multiplexing) and the like.Moreover, any conversion for effecting TDM (Time-Division Multiplexing)or FDM (Frequency Division Multiplexing), or OFDM (Orthogonal FrequencyDivision Multiplexing) is also an example of encoding. The encodedsignal is converted by the modulator 814 into a radio frequency signal,so as to be transmitted from the transmission antenna 815.

In the field of communications, a wave representing a signal to besuperposed on a carrier wave may be referred to as a “signal wave”;however, the term “signal wave” as used in the present specificationdoes not carry that definition. A “signal wave” as referred to in thepresent specification is broadly meant to be any electromagnetic wave topropagate in a waveguide, or any electromagnetic wave fortransmission/reception via an antenna element.

The receiver 820A restores the radio frequency signal that has beenreceived by the reception antenna 825 to a low-frequency signal at thedemodulator 824, and to a digital signal at the decoder 823. The decodeddigital signal is restored to an analog signal by the digital to analog(D/A) converter 822, and is sent to a data sink (data receiver) 821.Through the above processes, a sequence of transmission and receptionprocesses is completed.

When the communicating agent is a digital appliance such as a computer,analog to digital conversion of the transmission signal and digital toanalog conversion of the reception signal are not needed in theaforementioned processes. Thus, the analog to digital converter 812 andthe digital to analog converter 822 in FIG. 34 may be omitted. A systemof such construction is also encompassed within a digital communicationsystem.

In a digital communication system, in order to ensure signal intensityor expand channel capacity, various methods may be adopted. Many suchmethods are also effective in a communication system which utilizesradio waves of the millimeter wave band or the terahertz band.

Radio waves in the millimeter wave band or the terahertz band havehigher straightness than do radio waves of lower frequencies, andundergoes less diffraction, i.e., bending around into the shadow side ofan obstacle. Therefore, it is not uncommon for a receiver to fail todirectly receive a radio wave that has been transmitted from atransmitter. Even in such situations, reflected waves may often bereceived, but a reflected wave of a radio wave signal is often poorer inquality than is the direct wave, thus making stable reception moredifficult. Furthermore, a plurality of reflected waves may arrivethrough different paths. In that case, the reception waves withdifferent path lengths might differ in phase from one another, thuscausing multi-path fading.

As a technique for improving such situations, a so-called antennadiversity technique may be used. In this technique, at least one of thetransmitter and the receiver includes a plurality of antennas. If theplurality of antennas are parted by distances which differ from oneanother by at least about the wavelength, the resulting states of thereception waves will be different. Accordingly, the antenna that iscapable of transmission/reception with the highest quality among all isselectively used, thereby enhancing the reliability of communication.Alternatively, signals which are obtained from more than one antenna maybe merged for an improved signal quality.

In the communication system 800A shown in FIG. 34, for example, thereceiver 820A may include a plurality of reception antennas 825. In thiscase, a switcher exists between the plurality of reception antennas 825and the demodulator 824. Through the switcher, the receiver 820Aconnects the antenna that provides the highest-quality signal among theplurality of reception antennas 825 to the demodulator 824. In thiscase, the transmitter 810A may also include a plurality of transmissionantennas 815.

Second Example of Communication System

FIG. 35 is a block diagram showing an example of a communication system800B including a transmitter 810B which is capable of varying theradiation pattern of radio waves. In this exemplary application, thereceiver is identical to the receiver 820A shown in FIG. 34; for thisreason, the receiver is omitted from illustration in FIG. 35. Inaddition to the construction of the transmitter 810A, the transmitter810B also includes an antenna array 815 b, which includes a plurality ofantenna elements 8151. The antenna array 815 b may be an array antennaaccording to an embodiment of the present disclosure. The transmitter810B further includes a plurality of phase shifters (PS) 816 which arerespectively connected between the modulator 814 and the plurality ofantenna elements 8151. In the transmitter 810B, an output of themodulator 814 is sent to the plurality of phase shifters 816, wherephase differences are imparted and the resultant signals are led to theplurality of antenna elements 8151. In the case where the plurality ofantenna elements 8151 are disposed at equal intervals, if a radiofrequency signal whose phase differs by a certain amount with respect toan adjacent antenna element is fed to each antenna element 8151, a mainlobe 817 of the antenna array 815 b will be oriented in an azimuth whichis inclined from the front, this inclination being in accordance withthe phase difference. This method may be referred to as beam forming.

The azimuth of the main lobe 817 may be altered by allowing therespective phase shifters 816 to impart varying phase differences. Thismethod may be referred to as beam steering. By finding phase differencesthat are conducive to the best transmission/reception state, thereliability of communication can be enhanced. Although the example hereillustrates a case where the phase difference to be imparted by thephase shifters 816 is constant between any adjacent antenna elements8151, this is not limiting. Moreover, phase differences may be impartedso that the radio wave will be radiated in an azimuth which allows notonly the direct wave but also reflected waves to reach the receiver.

A method called null steering can also be used in the transmitter 810B.This is a method where phase differences are adjusted to create a statewhere the radio wave is radiated in no specific direction. By performingnull steering, it becomes possible to restrain radio waves from beingradiated toward any other receiver to which transmission of the radiowave is not intended. This can avoid interference. Although a very broadfrequency band is available to digital communication utilizingmillimeter waves or terahertz waves, it is nonetheless preferable tomake as efficient a use of the bandwidth as possible. By using nullsteering, plural instances of transmission/reception can be performedwithin the same band, whereby efficiency of utility of the bandwidth canbe enhanced. A method which enhances the efficiency of utility of thebandwidth by using techniques such as beam forming, beam steering, andnull steering may sometimes be referred to as SDMA (Spatial DivisionMultiple Access).

Third Example of Communication System

In order to increase the channel capacity in a specific frequency band,a method called MIMO (Multiple-Input and Multiple-Output) may beadopted. Under MIMO, a plurality of transmission antennas and aplurality of reception antennas are used. A radio wave is radiated fromeach of the plurality of transmission antennas. In one example,respectively different signals may be superposed on the radio waves tobe radiated. Each of the plurality of reception antennas receives all ofthe transmitted plurality of radio waves. However, since differentreception antennas will receive radio waves that arrive throughdifferent paths, differences will occur among the phases of the receivedradio waves. By utilizing these differences, it is possible to, at thereceiver side, separate the plurality of signals which were contained inthe plurality of radio waves.

The waveguide device and antenna device according to the presentdisclosure can also be used in a communication system which utilizesMIMO. Hereinafter, an example such a communication system will bedescribed.

FIG. 36 is a block diagram showing an example of a communication system800C implementing a MIMO function. In the communication system 800C, atransmitter 830 includes an encoder 832, a TX-MIMO processor 833, andtwo transmission antennas 8351 and 8352. A receiver 840 includes tworeception antennas 8451 and 8452, an RX-MIMO processor 843, and adecoder 842. Note that the number of transmission antennas and thenumber of reception antennas may each be greater than two. Herein, forease of explanation, an example where there are two antennas of eachkind will be illustrated. In general, the channel capacity of an MIMOcommunication system will increase in proportion to the number ofwhichever is the fewer between the transmission antennas and thereception antennas.

Having received a signal from the data signal source 831, thetransmitter 830 encodes the signal at the encoder 832 so that the signalis ready for transmission. The encoded signal is distributed by theTX-MIMO processor 833 between the two transmission antennas 8351 and8352.

In a processing method according to one example of the MIMO method, theTX-MIMO processor 833 splits a sequence of encoded signals into two,i.e., as many as there are transmission antennas 8352, and sends them inparallel to the transmission antennas 8351 and 8352. The transmissionantennas 8351 and 8352 respectively radiate radio waves containinginformation of the split signal sequences. When there are N transmissionantennas, the signal sequence is split into N. The radiated radio wavesare simultaneously received by the two reception antennas 8451 and 8452.In other words, in the radio waves which are received by each of thereception antennas 8451 and 8452, the two signals which were split atthe time of transmission are mixedly contained. Separation between thesemixed signals is achieved by the RX-MIMO processor 843.

The two mixed signals can be separated by paying attention to the phasedifferences between the radio waves, for example. A phase differencebetween two radio waves of the case where the radio waves which havearrived from the transmission antenna 8351 are received by the receptionantennas 8451 and 8452 is different from a phase difference between tworadio waves of the case where the radio waves which have arrived fromthe transmission antenna 8352 are received by the reception antennas8451 and 8452. That is, the phase difference between reception antennasdiffers depending on the path of transmission/reception. Moreover,unless the spatial relationship between a transmission antenna and areception antenna is changed, the phase difference therebetween remainsunchanged. Therefore, based on correlation between reception signalsreceived by the two reception antennas, as shifted by a phase differencewhich is determined by the path of transmission/reception, it ispossible to extract any signal that is received through that path oftransmission/reception. The RX-MIMO processor 843 may separate the twosignal sequences from the reception signal e.g. by this method, thusrestoring the signal sequence before the split. The restored signalsequence still remains encoded, and therefore is sent to the decoder 842so as to be restored to the original signal there. The restored signalis sent to the data sink 841.

Although the MIMO communication system 800C in this example transmits orreceives a digital signal, an MIMO communication system which transmitsor receives an analog signal can also be realized. In that case, inaddition to the construction of FIG. 36, an analog to digital converterand a digital to analog converter as have been described with referenceto FIG. 34 are provided. Note that the information to be used indistinguishing between signals from different transmission antennas isnot limited to phase difference information. Generally speaking, for adifferent combination of a transmission antenna and a reception antenna,the received radio wave may differ not only in terms of phase, but alsoin scatter, fading, and other conditions. These are collectivelyreferred to as CSI (Channel State Information). CSI may be utilized indistinguishing between different paths of transmission/reception in asystem utilizing MIMO.

Note that it is not an essential requirement that the plurality oftransmission antennas radiate transmission waves containing respectivelyindependent signals. So long as separation is possible at the receptionantenna side, each transmission antenna may radiate a radio wavecontaining a plurality of signals. Moreover, beam forming may beperformed at the transmission antenna side, while a transmission wavecontaining a single signal, as a synthetic wave of the radio waves fromthe respective transmission antennas, may be formed at the receptionantenna. In this case, too, each transmission antenna is adapted so asto radiate a radio wave containing a plurality of signals.

In this third example, too, as in the first and second examples, variousmethods such as CDM, FDM, TDM, and OFDM may be used as a method ofsignal encoding.

In a communication system, a circuit board that implements an integratedcircuit (referred to as a signal processing circuit or a communicationcircuit) for processing signals may be stacked as a layer on thewaveguide device and antenna device according to an embodiment of thepresent disclosure. Since the waveguide device and antenna deviceaccording to an embodiment of the present disclosure is structured sothat plate-like conductive members are layered therein, it is easy tofurther stack a circuit board thereupon. By adopting such anarrangement, a transmitter and a receiver which are smaller in volumethan in the case where a hollow waveguide or the like is employed can berealized.

In the first to third examples of the communication system as describedabove, each element of a transmitter or a receiver, e.g., an analog todigital converter, a digital to analog converter, an encoder, a decoder,a modulator, a demodulator, a TX-MIMO processor, or an RX-MIMOprocessor, is illustrated as one independent element in FIGS. 34, 35,and 36; however, these do not need to be discrete. For example, all ofthese elements may be realized by a single integrated circuit.Alternatively, some of these elements may be combined so as to berealized by a single integrated circuit. Either case qualifies as anembodiment of the present invention so long as the functions which havebeen described in the present disclosure are realized thereby.

A waveguide device and an antenna device according to the presentdisclosure are usable in any technological field that makes use of anantenna. For example, they are available to various applications wheretransmission/reception of electromagnetic waves of the gigahertz band orthe terahertz band is performed. In particular, they are suitably usedin onboard radar systems, various types of monitoring systems, indoorpositioning systems, and wireless communication systems where downsizingis desired.

While the present invention has been described with respect to exemplaryembodiments thereof, it will be apparent to those skilled in the artthat the disclosed invention may be modified in numerous ways and mayassume many embodiments other than those specifically described above.Accordingly, it is intended by the appended claims to cover allmodifications of the invention that fall within the true spirit andscope of the invention.

This application is based on Japanese Patent Applications No.2016-006384 filed Jan. 15, 2016, the entire contents of which are herebyincorporated by reference.

What is claimed is:
 1. A waveguide device comprising: an electricallyconductive member having an electrically conductive surface; a waveguidemember having an electrically-conductive waveguide face of a stripeshape opposing the electrically conductive surface, the waveguide memberextending along the electrically conductive surface; and an artificialmagnetic conductor extending on both sides of the waveguide member,wherein, the waveguide member has a bend at which a direction that thewaveguide member extends changes; a waveguide which is defined by theelectrically conductive surface, the waveguide face, and the artificialmagnetic conductor includes a gap enlargement where a gap between theelectrically conductive surface and the waveguide face is locallyincreased; and in a plan view projected along a direction perpendicularto the electrically conductive surface, at least a portion of the bendhas an overlap with the gap enlargement.
 2. The waveguide device ofclaim 1, wherein the waveguide member has a recess at the gapenlargement.
 3. The waveguide device of claim 2, wherein, the waveguidemember has an electrically-conductive side face connected to thewaveguide face; and a height of the electrically-conductive side face onan inside of the bend is lower in a place where the recess exists thanin a place adjacent to the recess.
 4. The waveguide device of claim 1,wherein the electrically conductive surface has a recess at the gapenlargement.
 5. The waveguide device of claim 2, wherein theelectrically conductive surface has a recess at the gap enlargement. 6.The waveguide device of claim 3, wherein the electrically conductivesurface has a recess at the gap enlargement.
 7. The waveguide device ofclaim 1, wherein, the waveguide member includes a first portion which isconnected to the bend and extends along a first direction, and a secondportion which is connected to the bend and extends along a seconddirection that intersects the first direction; at the bend, edges of thewaveguide face each include a transitory portion extending along adirection which is intermediate between the first direction and thesecond direction; and the transitory portion on an inside of the bend isshorter in length than the transitory portion on an outside of the bend.8. The waveguide device of claim 2, wherein, the waveguide memberincludes a first portion which is connected to the bend and extendsalong a first direction, and a second portion which is connected to thebend and extends along a second direction that intersects the firstdirection; at the bend, edges of the waveguide face each include atransitory portion extending along a direction which is intermediatebetween the first direction and the second direction; and the transitoryportion on an inside of the bend is shorter in length than thetransitory portion on an outside of the bend.
 9. The waveguide device ofclaim 4, wherein, the waveguide member includes a first portion which isconnected to the bend and extends along a first direction, and a secondportion which is connected to the bend and extends along a seconddirection that intersects the first direction; at the bend, edges of thewaveguide face each include a transitory portion extending along adirection which is intermediate between the first direction and thesecond direction; and the transitory portion on an inside of the bend isshorter in length than the transitory portion on an outside of the bend.10. The waveguide device of claim 5, wherein, the waveguide memberincludes a first portion which is connected to the bend and extendsalong a first direction, and a second portion which is connected to thebend and extends along a second direction that intersects the firstdirection; at the bend, edges of the waveguide face each include atransitory portion extending along a direction which is intermediatebetween the first direction and the second direction; and the transitoryportion on an inside of the bend is shorter in length than thetransitory portion on an outside of the bend.
 11. The waveguide deviceof claim 7, wherein, the waveguide member includes a portion with achamfered corner on the outside of the bend; and an upper edge of theportion with the chamfered corner is flush with the transitory portionon the outside of the bend.
 12. The waveguide device of claim 8,wherein, the waveguide member includes a portion with a chamfered corneron the outside of the bend; and an upper edge of the portion with thechamfered corner is flush with the transitory portion on the outside ofthe bend.
 13. The waveguide device of claim 9, wherein, the waveguidemember includes a portion with a chamfered corner on the outside of thebend; and an upper edge of the portion with the chamfered corner isflush with the transitory portion on the outside of the bend.
 14. Thewaveguide device of claim 7, wherein one end and another end of thetransitory portion on the outside of the bend are located inside the gapenlargement.
 15. The waveguide device of claim 9, wherein one end andanother end of the transitory portion on the outside of the bend arelocated inside the gap enlargement.
 16. The waveguide device of claim11, wherein one end and another end of the transitory portion on theoutside of the bend are located inside the gap enlargement.
 17. Thewaveguide device of claim 13, wherein one end and another end of thetransitory portion on the outside of the bend are located inside the gapenlargement.
 18. The waveguide device of claim 1, wherein the bend has abending angle of 90°.
 19. The waveguide device of claim 2, wherein thebend has a bending angle of 90°.
 20. The waveguide device of claim 4,wherein the bend has a bending angle of 90°.
 21. The waveguide device ofclaim 1 further comprising a further electrically conductive member,wherein, the artificial magnetic conductor includes a plurality ofelectrically conductive rods each having a leading end opposing theelectrically conductive surface, and the plurality of electricallyconductive rods are connected to roots of the further electricallyconductive member.
 22. The waveguide device of claim 21, wherein, thewaveguide member is connected to the further electrically conductivemember; and the further electrically conductive member, the waveguidemember, and the plurality of electrically conductive rods are parts of acontinuous single-piece body.
 23. The waveguide device of claim 21,wherein, the waveguide device is used for propagation of anelectromagnetic wave of a predetermined band; and a width of thewaveguide member, a width of each electrically conductive rod, a widthof a space between two adjacent electrically conductive rods, a distancefrom the root of each electrically conductive rod to the electricallyconductive surface, and a width of a space between an electricallyconductive rod that is adjacent to the waveguide member and thewaveguide member are all less than λm/2, where λm is a wavelength, infree space, of an electromagnetic wave of a highest frequency amongelectromagnetic waves of the predetermined band.
 24. An antenna devicecomprising: a waveguide device of claim 1; and at least one antennaelement that is connected to the waveguide device.
 25. An antenna devicecomprising: a waveguide device of claim 2; and at least one antennaelement that is connected to the waveguide device.
 26. An antenna devicecomprising: a waveguide device of claim 4; and at least one antennaelement that is connected to the waveguide device.
 27. A radarcomprising: the antenna device of claim 24; and a microwave integratedcircuit that is connected to the antenna device.
 28. A radar comprising:the antenna device of claim 24; and a microwave integrated circuit thatis connected to the antenna device.
 29. A radar comprising: the antennadevice of claim 26; and a microwave integrated circuit that is connectedto the antenna device.